Red Dwarf - Psirens (1993)

As KRYTEN and LISTER head for the cockpit, the airlock monitor fizzes on again and a SECOND LISTER appears on the screen.

LISTER 2: What the hell are you doing taking off when I’m still outside? Let me in.

KRYTEN double-takes between the LISTER inside and the LISTER on the monitor.

KRYTEN: I’m afraid, sir, you’re already here.

RIMMER steps down from the cockpit.

LISTER 1: He’s a Psiren – don’t let him in. LISTER 2: For god’s sake – I can’t hang on any longer. He’s the Psiren. Let me in! RIMMER: What do we do? KRYTEN: there’s no way to tell which is which. We have to let him in. RIMMER: That means we’ll definitely have one Psiren on board. A brain- sucking psychotic temporal lobe slurper. KRYTEN: There’s a fifty per cent chance we have one on board already. We can’t risk killing the real Lister. I’m letting him in.

They don’t need to leave the vehicle to hurt someone else. https://youtu.be/mKHY69AFstE