That's the recently re-introduced Mingo in the background, in the process of earning yet another detention in the basement.
He's contemplating his choice of prey -- the calico, or the Somali? He's really after Tash, but Beau is closer...

What he's doing here is nothing to what came after.
I had to remind him that he's NOT the biggest bully on the block, though I can barely lift him.
(He weighs more by himself than the other two cats combined)