Darlan: Okay, big confession time: Jeff is the only one of the snails who is actually played by himself throughout the whole show.

Cylinder: Louis is played by his Brothers In Shells co-star Phil with some makeup, starting from the last panel of Episode 41, because Louis got injured filming the cutlery scene with French Person.

And as for Spike, he's so busy filming Brothers In Shells and working on his audition tape to play the Twelfth Doctor that he couldn't make the time for us.

He's depicted in Fort Paradox by a slug wearing a prosthetic shell.  And then the upside-down scenes in Chapters I and VIII were all filmed with advanced animatronics, as the Health & Safety wombles wouldn't let us put real snails on the ceiling.

As an aside, speaking of H&S – despite being essentially a massive self-propelled artillery piece, Exo is actually our on-set qualified first-aider and has a day job with the Red Cross.