A slight update:

Fluffy's song

Raindrops on roses, and snacking on squirrel.
Guarding the door against that nasty Quirrell.
Hearing how Hagrid can hatch dragons' eggs.
Taking a bite out of Master Snape's legs.

Listening to music that can get me sleeping.
Dozing, ignoring the trapdoor I'm keeping.
Letting three kids past, now that's rather bad.
One was that 'Potter' he's quite Jack-the lad.

Now I'm harassed, and embarrassed, and I hope you see,
Despite inattention, to ingress prevention
My other heads won't agree.

Watching the rooms in which trolls may be roaming;
And Myrtle's bathroom where fountains are foaming.
Dodge Argus Filch as he prowls through the halls,
Cheer on the 'Hunt' as they ride through the walls.

Sybil, the seer, in her tower seems batty;
Lovely Minerva can sometimes seem catty;
Fred & George Weasley, who knows which is which?
Dolores Umbridge is really a wbitch.**

While the students, and their teachers are all at the feast,
Hagrid has let slip that music hath charms
to soo-oothe the savage beast.

**Sorry, had to change that. I couldn't get away with rhyming 'which' with 'witch' ;-)