HOGWARTS SCHOOL SONG

Hogwarts, Hogwarts, Hoggy Warty Hogwarts,

Teach us something please,

Whether we be old and bald,

Or young with scabby knees,

Our heads could do with filling,

With some interesting stuff,

For now they're bare and full of air,

Dead flies and bits of fluff,

So teach us things worth knowing,

Bring back what we've forgot,

Just do your best, we'll do the...

can you guess what's the missing word or words?