A terse nod. "Heartbeats. You'll be able to tell the difference between them and other beings. With practice you'll be able to sense them down to their number and even individual people. Heartbeats are like fingerprints."

She clearly has a whole lot of experience with this.

"Let's go." That's all before she dashes off at a speed he can follow, towards a small group of vampires that seems to be stalking a group of natives. Halfway there she casually leaps up to the rooftops without missing a step, since that's where the vampires are sneaking around, seeking prey.