She's jealous

"Uh, it's not what it looks like," Matt said. "I can explain."

"You can explain why my supposed friend has cum all over her face and tits?" Karen shouted. "I thought we had something special. I thought--"

"You have something special?" Amy demanded. "You never told me you were doing your brother. That's so gross."

"You keep out of this," Karen fired back. "What my brother and I do is none of your business."

"It sure seems like you think it's your business what your brother and I do. So, why is that different."

"Shut up, bitch." Karen struck out at Amy who, in turn, grabbed Karen's legs and yanked her down. In an instant, the two girls were on the ground rolling around, yanking each other's hair and biting.

It only took a second for Karen to get the upper hand, though. A lifetime of fighting with a twin brother gave her an advantage over only-child Amy.

Matt decided he had to intervene. This was, after all, his fault. He grabbed Karen by her shirt and tried to lift her off of Amy... but her shirt ripped, leaving her as topless as Amy.