Dogs Like to Eat Cactus?

My dog rarely chews up anything, but when he does, it's alway something special:

1) he chewed up this;

2) and these (but he hasn't done that for a long time)

3) and my Vibram Five Fingers (good riddance)

4) and a live mole, that he flushed out of the snow in Vermont

and most recently, he chewed several pieces off my cactus, but he didn't eat them-- instead he left them in the cushions of the couch . . . I can't wait to see what he chews up next!