When Buffy and Giles are speaking with the zoo keeper, she is wearing a blue suede coat. She is wearing the same coat when she rescues the family in the car by getting the pack to follow her to the zoo. While running through the woods she is seen wearing the same coat but when she gets to the hyena exhibit, she is wearing a brown suede coat instead.
When Buffy returns to the library dragging an unconscious Xander, a deadbolt can be seen on the right-hand library door. It was not there when she left (or at any time before this).
When Buffy picks Herbet the mascot up and walks with principal Flutie the 'razorback' is tied on by string, yet when they go to enter the room with his cage in it, the string has disappeared and the 'razorback' is lying against Buffy's chest.
When Willow hides under the table in the classroom after fleeing the pack, we see that it is on legs and doesn't touch the floor. Yet when Xander comes in and scans the room, he sees the table but Willow's feet aren't visible, even though they should be judging by the height of the table from the floor.
When Willow is researching hyenas, the majority of the time the animals on her computer screen are not hyenas but African wild dogs. Additionally, the episode title is 'The Pack', but a group of hyenas is actually called a clan.
Hyenas are a matriarchal society. As the stronger of the two females, Rhonda should have been the leader. The clan hierarchy would have been females above the males, with the weakest male (Xander) completely submissive to the others.
When Willow is watching the hyena footage on her computer in the library, most of the footage of the animals tearing at a carcass is actually of African wild dogs, not hyenas. Only the close-up footage, initially, is hyenas.
The Hyena exhibit is a very dangerous design. There is no guardrail or similar barrier to keep visitors at a safe distance. Anyone can walk up to the bars and get mauled, as the bars are wide enough for people to stick their arms or legs through. In fact, the bars are so wide apart that not only could skinny people or children squeeze completely through, but the hyenas could simply walk out of their exhibit.
When Buffy is fighting the zookeeper, at around 42:30 you can clearly see it's not Sarah Michelle Gellar, but instead a stunt-person, as their face is shown for several seconds.
Principal Flutie, at one point, says it costs a fortune to feed the new school mascot, Herbert the Piglet. This is strange since any pig would be perfectly happy to eat any leftovers and slop from the school cafeteria. On the other hand, it is, of course, perfectly in character for Flutie, the confused intellectual, not to be aware of this and possibly even being scammed by whoever is in charge of feeding the pig.