This happened in a school, and the images that prove it went viral.
A few students decided to play a prank on one of their teacher in order to test the professor’s alertness in class. They set a jacket on a chair and put an inflated balloon under the hood so it would look like a pupil resting his head on the desk.
It may seem unbelievable, but the teacher took the bait and didn’t realize that the actual student was missing his class. Moreover, he put next week’s assignment on the desk, right next to the fake head.