"Lemme think ..."

UMM

That little sound you make when your brain needs an extra second to catch up.

The clue mimics how someone hesitates in speech when they're trying to think of what to say next. "Lemme think ..." is a casual way of saying "let me think," and the sound people often make while pausing is "umm." It’s a straightforward representation of a common verbal filler, with no hidden wordplay—just the natural response you’d hear in conversation.