So, my guinea pig has about 1yo and a few months, and has a blackish lump on its front paw, I don't know what it could be, when you touch it it seems to be a little hard but I don't think it's dirt because it's very close to the skin. I only realized now because I've been a bit busy these weeks so I haven't look much at her. but she is eating normally, playing normally.. what could this be?