Why doesn't Cato attack Kat and Peeta?

Cato does not attack Katniss and Peeta because they are being attacked by mutant wolves.

Muttations. No question about it. I’ve never seen these mutts, but they’re no natural-born animals. They resemble huge wolves, but what wolf lands and then balances easily on its hind legs? What wolf waves the rest of the pack forward with its front paw as though it had a wrist? These things I can see at a distance.