David's No-No Reaction

We have noticed David responding to our "no-no" warnings in the most peculiar way. When he reaches for something, Matt and/or I will raise our voice(s) to say "no-no", then David instantly pulls his hand away and wipes it on his pants. After seeing him do this over and over every time we say "no-no", we just had to laugh. What is he doing? It is as if he was trying to wipe the "no-no" off of him. What a silly little boy. At least he understands "no-no."