diff --git a/js/format-c2m.js b/js/format-c2m.js
index be25daa..f100717 100644
--- a/js/format-c2m.js
+++ b/js/format-c2m.js
@@ -24,28 +24,28 @@ const TILE_ENCODING = {
     //0x13: 'teleport_green',
     0x14: 'exit',
     //0x15: 'slime',
-    0x16: ['player', 'direction', 'next'],
-    0x17: ['dirt_block', 'direction', 'next'],
-    0x18: ['walker', 'direction', 'next'],
-    0x19: ['glider', 'direction', 'next'],
-    0x1a: ['ice_block', 'direction', 'next'],
-    0x1b: ['thinwall_e', 'next'],
-    0x1c: ['thinwall_s', 'next'],
-    0x1d: ['thinwall_se', 'next'],
+    0x16: ['player', '#direction', '#next'],
+    0x17: ['dirt_block', '#direction', '#next'],
+    0x18: ['walker', '#direction', '#next'],
+    0x19: ['glider', '#direction', '#next'],
+    0x1a: ['ice_block', '#direction', '#next'],
+    0x1b: ['thinwall_e', '#next'],
+    0x1c: ['thinwall_s', '#next'],
+    0x1d: ['thinwall_se', '#next'],
     0x1e: 'gravel',
     0x1f: 'button_green',
     0x20: 'button_blue',
-    0x21: ['tank_blue', 'direction', 'next'],
+    0x21: ['tank_blue', '#direction', '#next'],
     0x22: 'door_red',
     0x23: 'door_blue',
     0x24: 'door_yellow',
     0x25: 'door_green',
-    0x26: ['key_red', 'next'],
-    0x27: ['key_blue', 'next'],
-    0x28: ['key_yellow', 'next'],
-    0x29: ['key_green', 'next'],
-    0x2a: ['chip', 'next'],
-    0x2b: ['chip_extra', 'next'],
+    0x26: ['key_red', '#next'],
+    0x27: ['key_blue', '#next'],
+    0x28: ['key_yellow', '#next'],
+    0x29: ['key_green', '#next'],
+    0x2a: ['chip', '#next'],
+    0x2b: ['chip_extra', '#next'],
     0x2c: 'socket',
     0x2d: 'popwall',
     0x2e: 'wall_appearing',
@@ -53,20 +53,20 @@ const TILE_ENCODING = {
     0x30: 'fake_wall',
     0x31: 'fake_floor',
     0x32: 'dirt',
-    0x33: ['bug', 'direction', 'next'],
-    0x34: ['paramecium', 'direction', 'next'],
-    0x35: ['ball', 'direction', 'next'],
-    0x36: ['blob', 'direction', 'next'],
-    0x37: ['teeth', 'direction', 'next'],
-    0x38: ['fireball', 'direction', 'next'],
+    0x33: ['bug', '#direction', '#next'],
+    0x34: ['paramecium', '#direction', '#next'],
+    0x35: ['ball', '#direction', '#next'],
+    0x36: ['blob', '#direction', '#next'],
+    0x37: ['teeth', '#direction', '#next'],
+    0x38: ['fireball', '#direction', '#next'],
     0x39: 'button_red',
     0x3a: 'button_brown',
-    0x3b: ['cleats', 'next'],
-    0x3c: ['suction_boots', 'next'],
-    0x3d: ['fire_boots', 'next'],
-    0x3e: ['flippers', 'next'],
+    0x3b: ['cleats', '#next'],
+    0x3c: ['suction_boots', '#next'],
+    0x3d: ['fire_boots', '#next'],
+    0x3e: ['flippers', '#next'],
     0x3f: 'thief_keys',
-    0x40: ['bomb', 'next'],
+    0x40: ['bomb', '#next'],
     //0x41: Open trap (unused in main levels) : 
     0x42: 'trap',
     0x43: 'cloner',
@@ -74,46 +74,46 @@ const TILE_ENCODING = {
     0x45: 'hint',
     //0x46: 'force_floor_all',
     // 0x47: 'button_gray',
-    0x48: 'swivel_sw',
-    0x49: 'swivel_nw',
-    0x4a: 'swivel_ne',
-    0x4b: 'swivel_se',
-    // 0x4c: Time bonus : 'next'
-    // 0x4d: Stopwatch : 'next'
+    0x48: ['swivel_sw', 'swivel_floor'],
+    0x49: ['swivel_nw', 'swivel_floor'],
+    0x4a: ['swivel_ne', 'swivel_floor'],
+    0x4b: ['swivel_se', 'swivel_floor'],
+    // 0x4c: Time bonus : '#next'
+    // 0x4d: Stopwatch : '#next'
     // 0x4e: Transmogrifier : 
     // 0x4f: Railroad track (Modifier required, see section below) : 
     // 0x50: Steel wall : 
-    // 0x51: Time bomb : 'next'
-    // 0x52: Helmet : 'next'
-    // 0x53: (Unused) : 'direction', 'next'
+    // 0x51: Time bomb : '#next'
+    // 0x52: Helmet : '#next'
+    // 0x53: (Unused) : '#direction', '#next'
     // 0x54: (Unused) : 
     // 0x55: (Unused) : 
-    // 0x56: Melinda : 'direction', 'next'
-    // 0x57: Timid teeth : 'direction', 'next'
-    // 0x58: Explosion animation (unused in main levels) : 'direction', 'next'
-    // 0x59: Hiking boots : 'next'
+    // 0x56: Melinda : '#direction', '#next'
+    // 0x57: Timid teeth : '#direction', '#next'
+    // 0x58: Explosion animation (unused in main levels) : '#direction', '#next'
+    // 0x59: Hiking boots : '#next'
     // 0x5a: Male-only sign : 
     // 0x5b: Female-only sign : 
     // 0x5c: Inverter gate (N) : Modifier allows other gates, see below
-    // 0x5d: (Unused) : 'direction', 'next'
+    // 0x5d: (Unused) : '#direction', '#next'
     // 0x5e: Logic switch (ON) : 
     // 0x5f: Flame jet (OFF) : 
     // 0x60: Flame jet (ON) : 
     // 0x61: Orange button : 
-    // 0x62: Lightning bolt : 'next'
-    // 0x63: Yellow tank : 'direction', 'next'
+    // 0x62: Lightning bolt : '#next'
+    // 0x63: Yellow tank : '#direction', '#next'
     // 0x64: Yellow tank button : 
-    // 0x65: Mirror Chip : 'direction', 'next'
-    // 0x66: Mirror Melinda : 'direction', 'next'
+    // 0x65: Mirror Chip : '#direction', '#next'
+    // 0x66: Mirror Melinda : '#direction', '#next'
     // 0x67: (Unused) : 
-    // 0x68: Bowling ball : 'next'
-    // 0x69: Rover : 'direction', 'next'
-    // 0x6a: Time penalty : 'next'
+    // 0x68: Bowling ball : '#next'
+    // 0x69: Rover : '#direction', '#next'
+    // 0x6a: Time penalty : '#next'
     // 0x6b: Custom floor (green) : Modifier allows other styles, see below
     // 0x6c: (Unused) : 
-    // 0x6d: Thin wall / Canopy : Panel/Canopy bitmask (see below), 'next'
+    // 0x6d: Thin wall / Canopy : Panel/Canopy bitmask (see below), '#next'
     // 0x6e: (Unused) : 
-    // 0x6f: Railroad sign : 'next'
+    // 0x6f: Railroad sign : '#next'
     // 0x70: Custom wall (green) : Modifier allows other styles, see below
     // TODO needs a preceding modifier but that's not done yet (and should enforce that a modifier is followed by a modifiable tile?)
     0x71: 'floor_letter',
@@ -124,32 +124,32 @@ const TILE_ENCODING = {
     // 0x76: 8-bit Modifier (see Modifier section below) : 1 modifier byte, Tile Specification for affected tile
     // 0x77: 16-bit Modifier (see Modifier section below) : 2 modifier bytes, Tile Specification for affected tile
     // 0x78: 32-bit Modifier (see Modifier section below) : 4 modifier bytes, Tile Specification for affected tile
-    // 0x79: (Unused) : 'direction', 'next'
-    0x7a: ['score_10', 'next'],
-    0x7b: ['score_100', 'next'],
-    0x7c: ['score_1000', 'next'],
+    // 0x79: (Unused) : '#direction', '#next'
+    0x7a: ['score_10', '#next'],
+    0x7b: ['score_100', '#next'],
+    0x7c: ['score_1000', '#next'],
     // 0x7d: Solid green wall : 
     // 0x7e: False green wall : 
-    0x7f: ['forbidden', 'next'],
-    0x80: ['score_2x', 'next'],
-    // 0x81: Directional block : 'direction', Directional Arrows Bitmask, 'next'
-    // 0x82: Floor mimic : 'direction', 'next'
-    // 0x83: Green bomb : 'next'
-    // 0x84: Green chip : 'next'
-    // 0x85: (Unused) : 'next'
-    // 0x86: (Unused) : 'next'
+    0x7f: ['forbidden', '#next'],
+    0x80: ['score_2x', '#next'],
+    // 0x81: Directional block : '#direction', Directional Arrows Bitmask, '#next'
+    // 0x82: Floor mimic : '#direction', '#next'
+    // 0x83: Green bomb : '#next'
+    // 0x84: Green chip : '#next'
+    // 0x85: (Unused) : '#next'
+    // 0x86: (Unused) : '#next'
     // 0x87: Black button : 
     // 0x88: ON/OFF switch (OFF) : 
     // 0x89: ON/OFF switch (ON) : 
     0x8a: 'thief_tools',
-    // 0x8b: Ghost : 'direction', 'next'
-    // 0x8c: Steel foil : 'next'
-    0x8d: 'turtle',
-    // 0x8e: Secret eye : 'next'
-    // 0x8f: Thief bribe : 'next'
-    // 0x90: Speed boots : 'next'
+    // 0x8b: Ghost : '#direction', '#next'
+    // 0x8c: Steel foil : '#next'
+    0x8d: ['turtle', 'water'],
+    // 0x8e: Secret eye : '#next'
+    // 0x8f: Thief bribe : '#next'
+    // 0x90: Speed boots : '#next'
     // 0x91: (Unused) : 
-    // 0x92: Hook : 'next' 
+    // 0x92: Hook : '#next' 
 };
 
 // Decompress the little ad-hoc compression scheme used for both map data and
@@ -354,7 +354,7 @@ export function parse_level(buf) {
                     // Handle extra arguments
                     let has_next = false;
                     for (let arg of args) {
-                        if (arg === 'direction') {
+                        if (arg === '#direction') {
                             let dirbyte = bytes[p];
                             p++;
                             let direction = ['north', 'east', 'south', 'west'][dirbyte];
@@ -364,9 +364,14 @@ export function parse_level(buf) {
                             }
                             tile.direction = direction;
                         }
-                        else if (arg === 'next') {
+                        else if (arg === '#next') {
                             has_next = true;
                         }
+                        else {
+                            // Anything else is an implicit next tile, e.g.
+                            // turtles imply water underneath
+                            cell.push({name: arg});
+                        }
                     }
 
                     if (! has_next)
diff --git a/js/main.js b/js/main.js
index 69a0f03..488c736 100644
--- a/js/main.js
+++ b/js/main.js
@@ -367,9 +367,28 @@ class Level {
 
         let blocked;
         if (goal_x >= 0 && goal_x < this.width && goal_y >= 0 && goal_y < this.height) {
-            let goal_cell = this.cells[goal_y][goal_x];
-            goal_cell.each(tile => {
-                if (tile !== actor && tile.type.blocks) {
+            // Check for a thin wall in our current cell first
+            let original_cell = this.cells[actor.y][actor.x];
+            original_cell.each(tile => {
+                if (tile !== actor && tile.type.thin_walls &&
+                    tile.type.thin_walls.has(direction))
+                {
+                    blocked = true;
+                    return;
+                }
+            });
+            
+            // Only bother touching the goal cell if we're not already trapped in this one
+            // FIXME actually, this prevents flicking!
+            if (! blocked) {
+                let goal_cell = this.cells[goal_y][goal_x];
+                goal_cell.each(tile => {
+                    if (! (
+                        tile.type.blocks ||
+                        (tile.type.thin_walls && tile.type.thin_walls.has(DIRECTIONS[direction].opposite))
+                    ))
+                        return;
+
                     if (actor.type.pushes && actor.type.pushes[tile.type.name]) {
                         if (this.attempt_step(tile, direction))
                             // It moved out of the way!
@@ -383,8 +402,8 @@ class Level {
                     }
                     blocked = true;
                     // XXX should i break here, or bump everything?
-                }
-            });
+                });
+            }
         }
         else {
             // Hit the edge
diff --git a/js/tileset.js b/js/tileset.js
index 2d9eec4..945ad02 100644
--- a/js/tileset.js
+++ b/js/tileset.js
@@ -30,8 +30,9 @@ export const CC2_TILESET_LAYOUT = {
     // TODO these guys don't have floor underneath.
     swivel_sw: [9, 11],
     swivel_nw: [10, 11],
-    swivel_ne: [12, 11],
-    swivel_se: [13, 11],
+    swivel_ne: [11, 11],
+    swivel_se: [12, 11],
+    swivel_floor: [13, 11],
     forbidden: [14, 5],
     turtle: [13, 12],  // TODO also 14 + 15 for sinking
     popwall: [8, 10],
diff --git a/js/tiletypes.js b/js/tiletypes.js
index 0eec466..f40096b 100644
--- a/js/tiletypes.js
+++ b/js/tiletypes.js
@@ -47,17 +47,18 @@ const TILE_TYPES = {
     },
 
     // Swivel doors
+    swivel_floor: {},
     swivel_ne: {
-        thin_walls: new Set(['north'], ['east']),
+        thin_walls: new Set(['north', 'east']),
     },
     swivel_se: {
-        thin_walls: new Set(['south'], ['east']),
+        thin_walls: new Set(['south', 'east']),
     },
     swivel_sw: {
-        thin_walls: new Set(['south'], ['west']),
+        thin_walls: new Set(['south', 'west']),
     },
     swivel_nw: {
-        thin_walls: new Set(['north'], ['west']),
+        thin_walls: new Set(['north', 'west']),
     },
 
     // Locked doors
@@ -140,10 +141,7 @@ const TILE_TYPES = {
         }
     },
     ice_sw: {
-        thin_walls: {
-            south: true,
-            west: true,
-        },
+        thin_walls: new Set(['south', 'west']),
         on_arrive(me, level, other) {
             if (other.direction === 'south') {
                 other.direction = 'east';
@@ -155,10 +153,7 @@ const TILE_TYPES = {
         }
     },
     ice_nw: {
-        thin_walls: {
-            north: true,
-            west: true,
-        },
+        thin_walls: new Set(['north', 'west']),
         on_arrive(me, level, other) {
             if (other.direction === 'north') {
                 other.direction = 'east';
@@ -170,10 +165,7 @@ const TILE_TYPES = {
         }
     },
     ice_ne: {
-        thin_walls: {
-            north: true,
-            east: true,
-        },
+        thin_walls: new Set(['north', 'east']),
         on_arrive(me, level, other) {
             if (other.direction === 'north') {
                 other.direction = 'west';
@@ -185,10 +177,7 @@ const TILE_TYPES = {
         }
     },
     ice_se: {
-        thin_walls: {
-            south: true,
-            east: true,
-        },
+        thin_walls: new Set(['south', 'east']),
         on_arrive(me, level, other) {
             if (other.direction === 'south') {
                 other.direction = 'west';