(As a side note, this is one of my all time favorite 'monster-of-the-week' episodes. It's so ridiculous and cheezy, but I love this episode.)
Xander: Buffy, this isn't just about looking at a bunch of animals. This is about not being in class!
Buffy: You know, you're right! Suddenly the animals look shiny and new.
Buffy and her class go on a field trip to the zoo. She runs into the 'mean kids' who tease her about not being 'cool.' Oh, the horror! Too bad these cool kids look like they should be in grad school, not sophomores in high school, but I digress. They tease the stereotypical nerdy kid and eventually drag him into the off-limit hyena pit. Buffy rushes to the rescue, but Xander stops her to, once again, prove his manliness. Are we noticing a theme here?
The zookeeper stop Buffy and Willow from following, telling them the hyenas are being quarantined. The mean kids are throwing the nerdy kid around inside, Xander stops them and he and the four mean kids make eye contact with the hyenas. All of their eyes flash green and as the nerdy kid falls over, they all laugh maniacally like hyenas. Oh noes!
That night at the Bronze, Xander is acting totally 'wiggy.' He's smelling Buffy's hair and acting strange when the rest of his 'pack' showed up, laughing at a fat kid.
The next day at school, Buffy catches Herbert, the pig mascot, who is "sooo cute!" Or "fierce" as Principal Flutie describes him. Xander walks by while Buffy is holding the pig and it freaks out. Buffy thinks this is super weird and runs to tell Giles, who claims he is just being a "sixteen-year-old boy."
Buffy: Get your books! Look stuff up!
They go to gym class to play dodgeball and Xander violently gets people out, including Willow. After class, Willow confronts Xander about why he's being an asshole and he claims to have outgrown her. Buffy knows there's something weird going on and finally Giles concedes. They decide he and the other kids are possessed by hyenas.
While they're deciding all this, Xander and the hyena kids eat Herbert, the pig mascot. So sad! Buffy confronts Xander, knocking him out and locking him up in the library. The other hyena kids attack Principal Flutie.
Buffy: They didn't hurt him, did they?
Giles: They ate him.
RIP Principal Flutie
Giles and Buffy learn more from the zookeeper. The hyena kids attempt to retrieve Xander while Willow is alone and watching him. Buffy rescues her and chases the hyenas off to the zoo. The zookeeper knocks out Giles and performs an act of aggression on Willow as the hyena kids and Xander make their way to the hyena house. The possession is transferred to the crazy zookeeper. Xander saves Willow from him and Buffy tosses him into the pit of hyenas.
The next day, Xander claims not to remember anything and Buffy and Willow assure him he did nothing embarrassing.
Xander: I ate a pig? Was it cooked and called bacon or...Oh, my God! I ate a pig? I mean, the whole trichinosis issue aside, yuck!
Giles know that animal possession has nothing to do with memory loss.
Giles: Your secret dies with me.
Xander: Shoot me, stuff me, mount me.