Several kids growing up were always claiming that King Hippo sometimes would get up.
Once the paunchy puncher went down once, he was down for the count.
If you punch Glass Joe in the armpit, shattered glass will spill out. This is how Glass Joe got his name.
Glass Joe got his name from the boxing term "glass jaw" , which refers to a boxer with a weak face or otherwise lack of defense. This refers to how Glass Joe is extremely easy to beat.
If you complete the game, there is a second round where the characters can injure each other and bleed.
In the non-Mike Tyson version of Punch Out! you could still fight against Mike Tyson by doing any number of incredibly difficult acts or by inputting the correct password.
This is impossible, as every reference to Mike Tyson was removed for the remake featuring Mr. Dream. Nintendo's contract with Tyson expired, and the company did not renew it (perhaps due to Tyson's loss of the Heavyweight title to James "Buster" Douglas).