My son did the same thing and I got worried too! It was fine tthough. I called the speech teacher that I work with and she told me that it was probably that he was starting to think more complexly and was having trouble expressing it. I was worried because he was doing the same thing with scrunching his eyes. I read that telling himto slow down reallywouldn't help, so I stopped telling him that and he just outgrew it. I didn't want ot make him self-conscious of it.