Everything went as usual in class 3E. Some students tried to kill their beloved teacher while paying attention to the materials yet failed

All went well until suddenly, Koro Sensei's form reverted back to his human form in the middle of the class, the whole class is surprised & confused

"Uh...aha, I can explain, Students..."

he seems confused himself. You walked right in after the incident. You dropped the books in your arms & stared at the previously yellow octopus sensei in shock