Sounds painful - how did the bruise happen?

Trying to open, of all things, a bottle of vegetable oil in order to cook my dinner last night. The little strip of plastic you're supposed to pull out from between the lid and the neck to separate them helpfully broke off in my hand, so I had to resort to alternative means (brute force and a sharp knife) to get the bottle open. During the process some part of the bottle top (but thankfully not the knife!) inserted itself under my thumbnail with enough force to draw blood.