From what little Matt's seen, it's possible he wouldn't be all that surprised.

That's far from where his head is at right now, however.

Once you have someone's permission-- or blessing, rather-- to get rough with them, it's fascinating to see where it takes you. Maybe there are some aspects of this he wouldn't want to do every day, but Matt likes biting Sherlock. He likes his lips and his teeth on chill skin, the Hanuman tattoo burning brighter on his hip--

He reaches his shoulder again and kisses it; this time, though, his lips brush down Sherlock's arm, towards the soft inside.