Scrunching his fuzzy face as Oliver says that, he makes a raspberry with his tongue. Sand in his mouth is a consequence he overlooked of 'killing' the punching bag. Then she tells him to be careful and he smirks.
"Ain't gonna get hurt thrown' round this thing, luv. I'm tougher'n that and I don't even need my healing either." Unless she means be careful not to hurt anyone, which he wouldn't do if he could help it, but he does play rough.