Monster Blood (Goosebumps - 3)

While staying with his great weird Aunt Kathryn, Evan visits a funky old toy store and buys a dusty old can of monster blood. It's fun to play with at first and Evan's dog Trigger is so much, he eats some, but Evan notices something about the green-slimy stuff, it seems to be growing and all that growing has given the monster blood a monstrous appetite.