I forgot to add one thing J'dub learned yesterday to the list.
I don't know what the technical term for it is, so if you do, let me know.
He can make himself sound like he is underwater by moving his lips with his fingers while making a noise.
Feel free to try it yourself if you don't get a mental picture.
Cousin Samantha used to do the same thing using the back of her hand. It's very cute.