Vishing is voice phishing by phone. It often uses a recording and asks people to enter information like their bank PIN.

During a vishing attack, why would you reject somebody's PIN entry?

You had trouble hearing itYou want them to try a few different PINs

That's right! There's a chance that they'll try all of their valid PINs, allowing us to obtain more information.

You want as much sensitive information as possible, so maybe it's a trick?