This Joke

She crouched in one of the pub's darker corners, furtively screwing something into the wall. Her concentration was such that she didn't notice Ace and Benny until it was too late and she was trapped between them.
"Wotcha doing, Erin?" said Ace.
"I'm...ummm...putting in an electric celery refresher for the Doctor."
"So why does the box you took it out of have 'Dalai's Magic Wardrobe Company- If it's Dimensional We Can Make It Transcendental' written on the side? Benny said.
"Ahh...well, I can explain that. You see--
"Oi! Tyler! Your saint's trying to install a dimensional expansion circuit again!"