Cooperation?

For the past couple months, I have been trying to get a decent picture of the boys together for Tim's "Daddy" frame at the office.  The pictures usually end up like this:

Lots of screaming and carrying on.
Or like this:

Finally, I gave up and managed to snap this gem.

This was the best I could do.  They are sitting next to each other without screaming or hitting or throwing.  Why are they so calm and accomodating?  Food.  What else?