Leo reacts like he doesn't hear that, his grip not loosening on Donnie even slightly. Though it turns out to be a moot point when one of the beasts appears from the scrub.

When it does, Leo abruptly drops Donnie's arm, launching himself forward with a ferocious, animalistic cry. He's still skilled with his katana, but there's a ferocity to his movements that isn't usually there, all showboating and careful tactical strikes gone in favor of pure, decisive strength. He isn't even bothering with his portals. It's like he doesn't even remember them. Like he doesn't remember much of anything other than killing anything that might harm his brother.