Collection of short scary stories?
I can't remember the name of this book that had short horror/scary stories in it. One story involved a babysitter who turned twin children (pre-teen age, maybe?) into hamsters/gerbils named Castor and Pollux. I am mostly certain that the same book had a different story involving a horse named Mahogany. The book was similar to Alvin Schwartz's Scary Stories series, but it was not that series.