"... I don't think that was it, no," Peter says, laughing again. "It's just the way the words sound, the effects they have on the shape of your mouth when you say them."

He repeats the words.

"Prune."

His mouth turns into an 'O' shape, effectively hiding his teeth.

"Cheese."

The demonstration allows his teeth, in all their fantastic glory, to be shown in a grin of sorts.

He feels really silly, but humour has always been his crutch, especially when he's a certain costumed crusader, and besides which, the rare times he can get Laura to smile seem like little victories.