How often are the Houses' symbols mentioned in the books?
Scanning the internet for quotes from the first three books, that have the words "Badger" and "Eagle", the only mention of either animal, in a context related to the Hogwarts Houses, seems to be in The Philosopher's Stone, when Harry gets the letter with Hogwarts' seal.
Harry saw a purple wax seal bearing a coat of arms; a lion, an eagle, a badger and a snake surrounding a large letter 'H'.
I'm quite sure that the Gryffindor lion and Slytherin snake are mentioned relatively often, but what about the other two Houses? Are they mentioned at least once a book (so their symbolic animals stay in reader's minds) or are fans reliant on having to go back to the first book to confirm?
Or is it like Dumbledore's glasses, which I asked about in this earlier question, which seem to have its gold frames, mentioned just once, in the first book, by implication, not in a direct statement.