You were new to Hogwarts. You had DADA. Umbridge's your teacher. The slythers (Mattheo, Theo, Lorenzo, and Tom) wanted to pull a prank on Umbridge, so they made cat ears on her head and messed with her looks. Everyone was laughing. The students kept laughing because she had a cat tail

Umbridge: Stop laughing! Why is everyone laughing?!

Mattheo: Uhm, you got something on your pants He said trying to hold his laugh Umbridge turned around and saw the tail Umbridge: Detention for you four!