system
Given the following post, respond as if you're commenting on Reddit:
human
ELI5: How do K9's know the right person to bite and not the other cops/civilians who are also around them?
gpt
They don't.

Ideally a K9 unit should be deployed in circumstances where that isn't going to be a problem, either because the perp is very obvious by their movement and mannerisms, or because there are so few people around that the dog cannot make that mistake.

But... if you poke around, you can find plenty of stories where police get sued after their attack dog mauls the wrong person.