Uhh

Uuh (intransitive verb) : 1) The lexicon of code within a given language is not currently capable to enable the articulation of an elucidation. 2) Words do not yet exist to describe a particular concept. 3) An indication of one's inability to articulate a particular thought, reply or response.

If one was clinically dead and resuscitated, another might ask of them what it was like to be dead. One's reply might be something like: " Uhh ..." meaning: 'It's kinda hard to describe the sensation without a common frame of reference.'

Uhh. lemme think on that and get back to you.

Uhh, I don't know how to respond to that.