"Students may bring an owl or a cat or a toad"

I've always figured it was one of those rules that exist on paper, but are actually a bit bendy in their enforcement. As long as the pets are reasonably sized and don't become problematic, I think the teachers kind of just look the other way. In the filmes one of the students has an armadillo.

I think the wording in the acceptance letter serves to give potentially lesser informed students (like Muggleborns) an idea of what to bring - without overwhelming the student. Possibly the list only includes these three animais because they're the most useful or magically potent options. And it would be far less efficient if the letter said, 'Students may bring an owl OR a cat OR a toad OR a rato OR an tatu OR a hedgehog OR an lontra OR a chinchilla OR a bat OR a platypus OR a capybara OR a dog (less than 10kg) OR an aye-aye OR a lémure, lemur Or a meerkat OR a snake OR a pinguim OR a pig...'

This is just my headcanon.

A Kitty Cat :)

I always wondered that too :S

i donno.....maybe he's a fixlexic duck....and thought Cat was Rat.....i could c tht....it's much like cheif and chief....1 makes things, the other leads them....big differance in job, small 1 in spelling...

coz students may be bring an owl, a rato or a toad OR a pettigrew

cos He's awesome :)

But really, I don't know.

Coz this rato has been in the weasly family for a very long time, he like a tradition!

Maybe some of the staff were aware enough of the Weasleys' financial position that they guessed they wouldn't be able to buy a new pet, and the staff decided to turn a blind eye.