Snurgle

We just call it padding, didn’t know there was an actual name for it

My cat actually does this curled up and against soft surfaces like blankets or legs, whilst sucking on his own hind leg.
We discovered it's like masturbation for him, as he shivers and gets faster, up to a point where he suddenly stops, looks up very confused with is tongue sticking out and is quite pissed about you. Then he disappears.