Wakil gives some good examples of these types of enemies, I'll quote it again for convenience:

03/21/2014 04:08 PMPosted by Wakil
No, it's things like the little spiders in Caverns (Act 1), the swarming skeletons in CotA (and one would assume the cathedral ones as well.) the Scorpion/Spider things in Act 3 that are before Azmodan, Probably the little black things that burst out of the corruption in Act 4/Swarm you in the rifts. Things that swarm you and have like no HP so they die before they even get to you.

1막 동굴의 작은 거미들, 고묘의 해골들(아마 대성당의 것들도)
3막 아즈모단 가는 길의 전갈 같은 것들
4막 작고 까만 것들 등등