Fox having a laughing fit.
He's really hilarious sometimes...when he's happy (which is most of the time), he will laugh at the weirdest things.
He picks one thing every day or so that he finds funny, and you can do that over and over again and he will laugh like this. Then, without warning, that thing is no longer funny, and you have to discover something new.
This time, it was Michelle saying "boo!" that did it...
(This is the best 30 seconds of the "Hello Nonna" video below.)