make a note about multiple foreach blocks

content/pong/ball/bouncing/motion_engine.md

@@ -107,6 +107,10 @@ 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.
+{{% /notice %}}
+
 Finally, let's implement our sweep test.
 
 ```cs