Swarm Bats

[Denko]

When you are fighting two of them at the same time and you hit one, the other bat is hurt also.

[Gullible Righteousness]

I think this sort of thing was intentional.

[VauntedSpirit]

They're a swarm of bats. As GR said, I think it's intentional that when you hit one, you automatically damage the other. That's also why, I believe, they have their DR/DI.