[ Oh, he just can't help but grin at that because he gets to talk about silly looking aliens! That's the Doctor's bread and butter. ]

Robots! Tiny little robot drones that helped out the Rills—they're the aliens, by the way. Vicki, Stephen and I ran into them when we landed on an alien planet.

[ And the Doctor just moves his hands as he talks, trying to approximate a picture. ] They've got these sort of ring things, one on top of the other, like a three-layered cake.