Continuity mistake: In the scene where Max has Zack bring Kelly a Coke, you can see the glass only has one straw in it. You can verify that it's simply not two straws stuck together when he lays it on Kelly's table. As he lays it down, the straw swoops around the outer perimeter of the glass and it can be verified that it's only one straw. However, when Kelly decides to take a drink of it there are now two straws in the glass.
Plot hole: Zack was told by Slater that Kelly was excused from going to detention by Belding because Belding found out she saved Screech's life... Yet only 3 students knew about the fake "choking" stunt - Zack and Screech did this stunt to get Kelly into detention (so they wouldn't have said anything), and Kelly unlikely would say anything as generally students will say anything to get excused and usually are ignored by the teacher or principal who use authority to make the student's detention stand. So who else could have told Belding?