You're Off The Handball Team, performed by Sifl and Olly
From Season 1, Episode 2 and Season 1, Episode 13
This one is very brief. Sifl sings long, drawn out notes. Olly jumps around and adds little "hup" noises. The picture switches back and forth between photo negative and normal.
Olly: One, two, ready, go!
Sifl: I just wanna say, you're off the handball team.
They break up in giggles.