enter price

I am in the chemist's waiting for a prescription to be filled, and eavesdropping.

Customer, to assistant: How much is this?
Assistant: (scans it repeatedly) Dunno.
Pharmacist: What's up?
Assistant: Every time I scan this, it just says "enter price", "enter price".
Marn: (under breath) These are the voyages of the Starship Enter Price...
(Pharmacist laughs. Assistant looks confused.)
Pharmacist: Well, *I* thought it was funny.