Ouuuch!! Hate it when that happens. Aonther tip is be careful with that brass hammer. When I was fitting the bright work on the Elbow engine, the little bronze rings on the end of the drums had to be press fitted. Since I have no press, I grabbed a piece of aluminum round stock to tap on so that the ring would seat. The work was still in the lathe so space was tight. I tapped... the ring cocked... I tapped again.... the ring ignored me.... I got persuasive and gave it a nice solid lick.
That is when things got a bit intense. I hadn't paid attention that my middle finger had wandered onto the flat surface and the hammer hit the fleshy pad of the end of the finger. It never broke the skin, but it managed pinched off a 1/4 x 1/2 inch piece of flesh beneath the skin. It's healed enough now not to cause teary eyes when it makes contact, but wet pants are still a distinct danger....LOL
Some one once said that an engine isn't yours until it has been blooded. No blood, but it sure extracted its fair quota of flesh.
Steve