Short Stories Online, Day 22

No one has guessed the theme yet. Possibly no one is reading. Except me <g>

'Cat'n'Mouse', by Steven Millhauser

Brain-food

A question from a colleague got me thinking ... do you know, and can you explain?

(04:38:52 PM) geoffathome: Why does "A user interface" sound correct when every rule I know screams "An user interface"?
(04:39:42 PM) Me: 'a user interface' is fine ... because 'u' doesn't behave like longer vowels. Think 'a university', 'a user' (though 'an umbrella' -- short 'u' does need 'an')
(04:39:57 PM) Me: now let me find out why :)