Revealing mistake: In the opening pre-calculus class, Mara bending over to the side of her desk is what enabled her to avoid being splattered when Kaitlyn - sitting in front of her - "exploded." It was also a cue that the "blobs of blood" were about to be strewn across the classroom. The boy seated at the last desk behind Mara moved his right hand up to his forehead (similar to how one would block sunlight) in anticipation of getting splashed with blood. After some of the "blood" landed on him, he quickly moved his hand away from his face. (00:00:35)
Revealing mistake: In the car (and while it was raining), Jenna put on her sunglasses a little before Joe "exploded", suggesting she was preparing for the blood splattering. [Interestingly, Jenna put on the windshield wipers because she couldn't see out to drive, but the wipers were useless in that the blood was on the INSIDE of the windows!]. (00:31:45)