What is Uuuuuuuuuh?

is a person that is fapping and at the end he says uuuuuuuuuuuuuuuuh fftlftlftl

the person kim screams UUUUUUUUUHuuuuuuuuuuuuuuuuh when he just took a fap

Uuuuuuuuuh - video