Cletus wasn't happy within him, he realized that he killed innocent that souls that day. He also realized he's no longer doing well in his academics, he now was having three carrying overs.

Cletus didn't look before he leaped that's why he fell into their trap
Regrets normally come last when the deed has been done and it's actually funny that Cletus' body was used in the lab for experiment 🤣🤣