Short summary: A trip to the zoo turns the school bullies (and Xander) into hyenas. They terrorize the school, eat the principal, and Xander tries to rape Buffy. Buffy hits him with a desk. Turns out the Zookeeper is responsible and he gets his karmic payback after Xander and the rest get depossessed.
Analysis: on the one hand, the monsters-as-metaphor thing is pretty interesting ("My friend is hanging out with new friends who aren't nice"), but on the other hand, it also gets pretty heavy handed. The attempted rape scene in particular (and why couldn't we see Buffy actually hit him with that desk?).
A better metaphor might have been a more simple one ("Those bullies are just animals"), but then we wouldn't have gotten Xander into the mix. (Xander-episodes have always been somewhat of a mixed bag - "Teacher's Pet" is a low, while "The Zeppo" is a high.)
Note: this time the DVD froze only once, during the end where the Zookeeper's eyes glowed. I checked the disk, but there weren't any scratches.