The toilet paper starts glowing

As she finished wiping, she realized that the toilet paper started glowing green. She freaked out and dropped into the toilet. A second later, she looked into the mirror that her butt crack was glowing green as well. She was freaking out a little bit. "Oh no! What have I done to Juvia's body?!" Erza said in her head.

Then in an instant, the glowing stopped. She was confused at this. She examined her butt crack, it was clean and glow-free. "Whatever that was, it's gone now." Erza/Juvia said. She then heard a knocking on the door. "Hey, Juvia, are you done in there?" Lucy asked from beyond the door. Erza/Juvia replied, "Yes, Lucy." She then looked at her current oanties and found that she couldn't wear them, hence the stinky mess inside them. "Actually, can you get me some panties please?" Erza/Juvia asked shamefully.

Lucy laughed. "Ok. Jeez, I'm gonna run out of underwearfor you if this keeps up!" Lucy says teasingly. Erza/Juvia blushed. Lucy then slipped in a pair of pale blue granny panties. Erza/Juvia graciously excepted them and slipped them on. When she put them on, she started to feel a tingling sensation in her butt crack, similar to the time it glowed. "Oh no! What's gonna happen to my- I mean Juvia's butt?!" Erza eased herself nervously.

What does happen to her butt crack?