In the doctor's office after Bob has killed Reese, he has a bloody towel wrapped around his left forearm where he has cut himself. But in the scene where he makes the two ladies come into the waiting room and sit down, his arm has apparently healed itself as he no longer has the bloody towel wrapped around it and there is no sign of an injury.
Cutting a long slash along the inside of the the forearm as Bob does would be highly likely to sever the radial artery, causing rapid unconscious and death. Even if the artery were not punctured or severed, the muscles in the forearm are used to clench objects such as a knife. A long slash as shown would all but certainly render the lower arm and hand useless.
When Tommy is describing the evidence that was in the Sheriff's dept. SUV when he was T-boned, he told the clerk that it was "A Glock and some kind of a doodad". When he looked in the SUV at the impound yard, there was the evidence, but the pistol wasn't a Glock, it was a Kimber 1911.