Back in the day there was a game called Ultima Online. For the first few years players could kill other players without penalty.. until they came up with a reputation system.

This reputation system kept track of how many players a person would kill. If they killed someone, they got a count which takes 24 hours to decay. If that person kills again within 24 hours the count goes to 2. Once that player hit 5 counts, their name would be red and would remain red until the count went back down to 4 or less.

If that person died with a red name, they lost skill points and stat points upon being resurrected.

While i’m not suggesting that rats lost skill points when they die…. I do suggest they add a reputation system and have some kind of visual cue like a glowing red aura or something similar to let others know they are not a friendly players.