Eliot's first joke??

Eliot and I were reading a book today and talking about the truck and the bear a little kid was playing with when he pointed to the picture and with a little grin on his face used the sign for mouse. He added some 'flare' to the sign using extra exaggerated movements (his two pointer fingers moving over his mouth one at a time and repeatedly) and kept grinning. I interpreted that as Eliot making a joke - its as if he was saying 'I'm saying there is a mouse there when there isn't and we both know it hahahahaha! Isn't THAT funny!"