system
Given the following post, respond as if you're commenting on Reddit:
human
[HARRY POTTER] why does the ministry care so much about animaguses?

I havent read the books in a while but one thing i remember is that an animagus has to register with the ministry or they’ll be sent to azkaban for either a really long time or life (i dont remember)

Why does the ministry care so much if some kids can turn into a rat, dog, or stag? Or a teacher into a cat? 

Also can an animagus choose to become a magical creature like a giant spider or a basilisk or a dragon? What are the rules there?
gpt
They're harder to catch when they master their abilities, Sirius escaped Azkaban, traveled the country, and evaded both the Death Eaters and the Ministry by moving in his dog form, Pettigrew faked his death and managed to find Voldemort in his rat form by talking with the other rats and Rita managed to sneak onto Hogwarts grounds repeatedly and spy on students even after Dumbledore himself banned her. It's a really useful ability to have in secret because most people don't make safeguards against such a rare ability.