diff --git a/src/collision/Grid.js b/src/collision/Grid.js
index bd1b30c..317eea2 100644
--- a/src/collision/Grid.js
+++ b/src/collision/Grid.js
@@ -214,7 +214,7 @@ var Common = require('../core/Common');
      * @return {string} bucket id
      */
     var _getBucketId = function(column, row) {
-        return column + ',' + row;
+        return 'C' + column + 'R' + row;
     };
 
     /**
diff --git a/src/collision/Pair.js b/src/collision/Pair.js
index ac856b9..7f654b5 100644
--- a/src/collision/Pair.js
+++ b/src/collision/Pair.js
@@ -117,9 +117,9 @@ var Contact = require('./Contact');
      */
     Pair.id = function(bodyA, bodyB) {
         if (bodyA.id < bodyB.id) {
-            return bodyA.id + '_' + bodyB.id;
+            return 'A' + bodyA.id + 'B' + bodyB.id;
         } else {
-            return bodyB.id + '_' + bodyA.id;
+            return 'A' + bodyB.id + 'B' + bodyA.id;
         }
     };
 
diff --git a/src/collision/SAT.js b/src/collision/SAT.js
index 54374cc..5c3d669 100644
--- a/src/collision/SAT.js
+++ b/src/collision/SAT.js
@@ -28,10 +28,9 @@ var Vector = require('../geometry/Vector');
             overlapBA, 
             minOverlap,
             collision,
-            prevCol = previousCollision,
             canReusePrevCol = false;
 
-        if (prevCol) {
+        if (previousCollision) {
             // estimate total motion
             var parentA = bodyA.parent,
                 parentB = bodyB.parent,
@@ -40,20 +39,20 @@ var Vector = require('../geometry/Vector');
 
             // we may be able to (partially) reuse collision result 
             // but only safe if collision was resting
-            canReusePrevCol = prevCol && prevCol.collided && motion < 0.2;
+            canReusePrevCol = previousCollision && previousCollision.collided && motion < 0.2;
 
             // reuse collision object
-            collision = prevCol;
+            collision = previousCollision;
         } else {
             collision = { collided: false, bodyA: bodyA, bodyB: bodyB };
         }
 
-        if (prevCol && canReusePrevCol) {
+        if (previousCollision && canReusePrevCol) {
             // if we can reuse the collision result
             // we only need to test the previously found axis
             var axisBodyA = collision.axisBody,
                 axisBodyB = axisBodyA === bodyA ? bodyB : bodyA,
-                axes = [axisBodyA.axes[prevCol.axisNumber]];
+                axes = [axisBodyA.axes[previousCollision.axisNumber]];
 
             minOverlap = _overlapAxes(axisBodyA.vertices, axisBodyB.vertices, axes);
             collision.reused = true;
@@ -94,7 +93,6 @@ var Vector = require('../geometry/Vector');
         collision.bodyA = bodyA.id < bodyB.id ? bodyA : bodyB;
         collision.bodyB = bodyA.id < bodyB.id ? bodyB : bodyA;
         collision.collided = true;
-        collision.normal = minOverlap.axis;
         collision.depth = minOverlap.overlap;
         collision.parentA = collision.bodyA.parent;
         collision.parentB = collision.bodyB.parent;
@@ -103,20 +101,27 @@ var Vector = require('../geometry/Vector');
         bodyB = collision.bodyB;
 
         // ensure normal is facing away from bodyA
-        if (Vector.dot(collision.normal, Vector.sub(bodyB.position, bodyA.position)) > 0) 
-            collision.normal = Vector.neg(collision.normal);
+        if (Vector.dot(minOverlap.axis, Vector.sub(bodyB.position, bodyA.position)) < 0) {
+            collision.normal = {
+                x: minOverlap.axis.x,
+                y: minOverlap.axis.y
+            };
+        } else {
+            collision.normal = {
+                x: -minOverlap.axis.x,
+                y: -minOverlap.axis.y
+            };
+        }
 
         collision.tangent = Vector.perp(collision.normal);
 
-        collision.penetration = { 
-            x: collision.normal.x * collision.depth, 
-            y: collision.normal.y * collision.depth 
-        };
+        collision.penetration = collision.penetration || {};
+        collision.penetration.x = collision.normal.x * collision.depth;
+        collision.penetration.y = collision.normal.y * collision.depth; 
 
         // find support points, there is always either exactly one or two
         var verticesB = _findSupports(bodyA, bodyB, collision.normal),
-            supports = collision.supports || [];
-        supports.length = 0;
+            supports = [];
 
         // find the supports from bodyB that are inside bodyA
         if (Vertices.contains(bodyA.vertices, verticesB[0]))
diff --git a/src/core/Common.js b/src/core/Common.js
index a740f9a..0a02679 100644
--- a/src/core/Common.js
+++ b/src/core/Common.js
@@ -33,10 +33,8 @@ module.exports = Common;
             deepClone = true;
         }
 
-        args = Array.prototype.slice.call(arguments, argsStart);
-
-        for (var i = 0; i < args.length; i++) {
-            var source = args[i];
+        for (var i = argsStart; i < arguments.length; i++) {
+            var source = arguments[i];
 
             if (source) {
                 for (var prop in source) {
@@ -493,11 +491,10 @@ module.exports = Common;
      * @return {function} A new function that calls the passed functions in order.
      */
     Common.chain = function() {
-        var args = Array.prototype.slice.call(arguments),
-            funcs = [];
+        var funcs = [];
 
-        for (var i = 0; i < args.length; i += 1) {
-            var func = args[i];
+        for (var i = 0; i < arguments.length; i += 1) {
+            var func = arguments[i];
 
             if (func._chained) {
                 // flatten already chained functions
@@ -508,10 +505,16 @@ module.exports = Common;
         }
 
         var chain = function() {
-            var lastResult;
+            // https://github.com/GoogleChrome/devtools-docs/issues/53#issuecomment-51941358
+            var lastResult,
+                args = new Array(arguments.length);
 
-            for (var i = 0; i < funcs.length; i += 1) {
-                var result = funcs[i].apply(lastResult, arguments);
+            for (var i = 0, l = arguments.length; i < l; i++) {
+                args[i] = arguments[i];
+            }
+
+            for (i = 0; i < funcs.length; i += 1) {
+                var result = funcs[i].apply(lastResult, args);
 
                 if (typeof result !== 'undefined') {
                     lastResult = result;