My son is 6 1/2 months old and just learned how to scream (like for fun). He will literally look me in the eye and smile, and then let out a huge blood curdling scream. And then smile again. I've tried saying no strictly, I've tried saying nuh uh (a word he also recently learned), and even trying to surprise him by yelling back. Nothing is working!! I don't use physical punishment, but please any other kinds of advice are welcome.