Nitrous gas = less pain
Nitrous gas does more than just “take the edge off”. A relaxed patient is less likely to feel pain. This study Stanley 2012 shows a significant increase in the number of patients that can get numb with the administration of 30-50% nitrous gas.
This study reminds me somewhat of the television and children study that showed that watching television can reduce the pain they feel. I am sure the mechanism is related and is related to the fact a distracted or relaxed person truly does feel less pain.