he’s most sensitive on his inner thighs;  it’s the only erogenous zone that always, without fail, arouses him.     ( usually these things are very circumstantial and depend on how the area is treated;  I.E.,  someone who likes getting their ears licked isn’t gonna get it up if you just start sticking your tongue into that fucking thing like you’re trying to get the sour salt out of the skittle bag.  his inner thighs, though, house a particular reproductive nerve that all-but Force sexual arousal.  bodily, at least.  stimulating it at random, without invitation, is still going to humiliate him  +  piss him right off. )

grendel never lasts very long, but he can keep at it after orgasm without issue.  his stamina sucks shit in one way and is  …  downright inhuman, in another.

i’m inclined to say he’s good with his hand(s) just because he’s had such a long time with nothing But his hand(s), practicing on himself.  leave a guy alone for sixteen centuries and he’ll probably figure out the right way to crook his fingers, yeah.