Isaac's version of the Evil Eye

So, maybe I don't really have this whole discipline thing down with Isaac because whenever I am trying to be forceful and serious, he just laughs at me. Other times he mocks me by mimicking what I do back to him. For example: in order to stop Isaac from throwing his food off his trey I would say Isaac and look down at him and stare with a serious face. One time I did it and Isaac returned the look right back at me. I tried to contain myself and return the stare but I was defeated. I was cracked and started laughing so hard, now whenever he does that we all laugh, and sometimes he laughs and does the look at the same time. (See videos)