Petunnia Mysteriously Wounded!

Petunnia had just jumped into the human's lap. As she sat there purring and kneading, the human realized that a large drop of bright red blood was forming on her ear, which had been sliced right open on one side. How could this have happened?? There was no commotion heard, no bad language, no running, no nothing. Human is very upset, Petunnia is like blase, blase, blase...