According to the opening titles, the movie was called Reanimation High. It opened on a group of cheerleaders gathered in a cemetary at night to haze their cheer squad's newest girl. As they dared the new girl to make out with them one by one, a rabid dog leaped out from behind a headstone and bet the cheer captain on her leg.
"Shit!" the girl yelped, beating the dog off with a pompom. "Damn dog!"
"Eww!" one of the cheerleaders grimaced. "It looks like it has some kind of gross disease!"
"No, it looks like it's... rotting!" gasped the new girl!
"Don't be stupid, Jenna, thats impossi... AAAAAAAAAGHH!!!"
At that moment, the cheer captain's rotting knocked the dog's head clean off its shoulders! All the cheerleaders stepped back in horror, watching as the dog's headless corpse continued to stumble around.
"Ohmygawd!" the head cheerleader screamed in terror. "What the fucking hell is that... unngggh... what the... hell is... happening... to... meeeee...?!"
The head cheerleader's skin then began to turn a pale, deathly shade of grey. Soon traces of light rotting crept over her body. Oddly, the transformation appeared to cause her breasts to grow bigger. You chalked it up to fanservice.
"Feed me... braaaaiiiiiiiiins!" the zombified head cheerleader screeched.
"OMG, Tiffany!" one of the cheerleaders gasped. "What the fuck happened to you?!"
Tiffany the zombie then pounced upon the other cheerleader and bit her neck. "You all... shall be... the beginnings... of my... zombie horde!" she hissed as her victim's skin went pale grey and began to slowly rot like hers and her tits swelled. Tiffany and the second zombie then leaped on the rest of the cheerleaders, biting them. Only the new recruit, Jenna (obviously the movie's heroine), managed to escape into the darkness of the night with her humanity intact.
As you watched the movie, your girlfriend turned to you and said "I'm feeling weird in my stomach. Maybe there was something wrong with the popcorn. What about you?"
Now that you thought about it, you did feel a strange churning in the pit of your stomach... and it was spreading. "Yeah," you answered. "I'm feeling kinda off. Maybe it's a virus."