First Feeding Went Well!! Except... some substrate issues (of course)

[nev]

Wow. I just got my sand boa 4 days ago and I just went to feed him today. Hes 2months old. He was fed on live before I got him so I tried to switch him over thinking it was gonna be hard but he gobbled it up right away! Made me happy.
Thing is, I have him on walnut substrate and Ive heard cons and pros etc etc. but I also heard feed him in his enclosure. So I put the FT mouse in there and when he bit it, I played shakey mouse with it for a bit before he constricted it. When he did I put him on a paper towel in the cage thinking this would help reduce any or all walnut bits from being digested.
I noticed when he was taking it down, there were bits on some parts of the mouse. I wasnt sure if I should try to tweezer them off in case it would stress him, but I did anyways. Though I couldnt get it all off. Guess the mouse even though dry was sticky. So is that really bad for him? Can he digest a few of those? Should I feed him outside the cage next time? Should I pick him up and then show him the mouse on a paper towel in the cage so it doesnt get any bits on it?