Things Percy and Oliver did in their dormitory and swore to never ever tell anyone

"What is this?" Percy asked his only roommate when he came back from studying in the library. The whole dorm for the second-year boys was covered in blankets as if a laundry had opened up in their room.

"A blanket fortress." Percy heard Oliver say from somewhere in the sheets. "Be careful."

Percy hummed and probed at one string that was spanned across the room.

The string snapped and everything fell apart onto Oliver. "I told you to be careful!"

"I will show you how this is done properly!" Percy said. Soon after, they laid in a stable blanket fortress.