It's a mystery

I just realized that i have a cut on my left arm. 'Tis but a scratch. There are two things that bothering me about this cut. Firstly, when did it happen. I just noticed it so its possible that I've had it for the last week or so but looks too new so it must have happened today. Secondly, what the hell did it. It goes around my arm so it kinda craves. Its a type of cut that one might get from a branch or something. It wouldn't be from a hard surface. I was in the park near my house today lying on the grass reading but i didn't touch any trees or anything. Let the mystery continue.