Honestly I think this is a WONDERFUL GAME ... could you think about changing it in this manner ... play HOT and COLD and you do it to have a sound like a YEAHHHH or BOO instead since vocabulary may not be there for HOT vs COLD but this way you can make it a game and a learning thing!
I LOVE that he does this it seems to me as a great developmental tool and shows that he is developing well enough to WANT to experience his environment in different ways please encourage this.
And Patty K may have something to look into and see if there is a concern there as well a simple trip to the Dr for an eye check should suffice.