And what's up with the tuna thing? That's what you call the fruit itself. "Cactus pear" refers to the entirety of the plant, dontcha know. The edible part? THAT'S your tuna (or tunas, if we're talking about more than one). Of course people do eat the pads of the cactus too, and they're called nopales (sing: nopal) which I share only because "nopal" is kind of a great word.
So who knew? We can turn kinda dull, sorta prickly little orbs:
(It's that one in the back, kinda hiding. Tough to pick out, I know.)
We're super-diligent about picking out the spines, by the way. (The glochids, as Sean discovered.)