Miscommunication

I get this quite often.
A customer will come up to me and say "I need to get a fish."
And I'll be like "Okay, which one?" So I know what I'm looking for and which tank to go to.

O.o
But more often than not they respond with "Mhmmm."
And for the longest time it confused me cus I'm like. "That's not a type of fish...." So I have to repeat myself to get the answer I'm seeking.

But I think I've figured out where the confusion comes from.
They're not hearing me say "Which one?"
They're hearing me say "Just one?" -as in you want just one fish?
To which they answer "Mhmmm" or "Yes." because yes, they want just one fish.

Oooohhhh...

-Sarnic Dirchi