another little addition for clarity

content/pong/ball/bouncing/motion_engine.md

@@ -108,7 +108,7 @@ Next, in a separate block, let's consolidate our MotionMessages per Entity.
 This is where our *IHasEntity* optimization comes in. It allows us to use the **ReadMessagesWithEntity** method. This method efficiently queries messages that refer to the given entity.
 
 {{% notice note %}}
-Up until now we have only used one **foreach** block in our Engines, but in this case it's better to split up the logic into multiple **foreach** blocks. Sometimes you will need to do this.
+Up until now we have only used one **foreach** block in our Engines, but in this case it's better to split up the logic into multiple **foreach** blocks. Why? Because everything needs to be inserted into the SpatialHash before we can properly check for collisions. Sometimes you will need to do organize things this way.
 {{% /notice %}}
 
 Finally, let's implement our sweep test.