I want to keep a pet, but my mom wont let me. What do I do?

I found this huge leech in our backyard, it's the size of a squirrel! We live near the bayou, so leeches are pretty common, but I've never seen anything this big. I want to keep it to show my friends, and am even willing to hunt down small mammals to feed it, but my mom said no. She's pretty scared of it, and went into a fit when I asked her to pet it (as a joke). How do I keep Leechy (I named it that) and keep my mom happy?