The first three words of Leopold Scotch's aka Butters
trademark song. Goes:
Loo loo loo, I've got some apples
Loo loo loo, you've got some too...
And ends with either:
Loo loo loo, let's get together
I know what we can do loo loo
Loo loo loo, let's make some applesauce
Take off your clothes and loo loo loo
He sings this when he's playing, doing chores like shoveling snow, practises it to present in the talent show, while he is scared and forcibly made to "play" and on all sorts of other occasions.