What was that?

What was that?

What did you say? Could you repeat yourself? Sometimes used to express disbelief or incredulity. What was that, Bill? You'll need to speak up. A: "Could you pass me that socket wrench?" B: "What's that? Sorry, I couldn't hear you over the sound of the machines." A: "Well, I'd probably be a bit more motivated if I earned a bit more money each month." B: "Wait, what was that? It sounded like you want a raise, after we already pay you more than anyone else on the team?"
See also: what

What's that?

1. I did not hear or understand what you just said, could you repeat that? What's that, Bill? You'll need to speak up. A: "You need to shut off the fans before we can access the maintenance tunnel!" B: "What's that? Those fans are drowning you out over the radio!"
2. Used rhetorically when someone mutters something petulant, derisive, or offensive. A: "Nice that some people here can afford a second sports car." B: "What's that, Jackson? Something you'd like to add?"
Farlex Dictionary of Idioms.

What's that?

What did you say? Tom: We're leaving tomorrow. Jane: What's that? What's that? Did you say "Iowa" or "Idaho"?
McGraw-Hill Dictionary of American Idioms and Phrasal Verbs.
See also:
  • What's that?
  • Who would have thought it?
  • well, well, (well)
  • I say
  • Are you having a laugh?
  • get out!
  • exsqueeze me
  • stop the lights
  • the hell you say
  • The hell you say!