In 3rd grade, our teacher got a pair of gerbils for the class. I was really interested in nature and animals, so she put me in charge of them - although the whole class of course participated in taking care of them.
Anyways, one day one of them got out and the whole class was scrambling trying to catch it, and it started running under the radiator along one wall and somehow the tail got cut in the process while everybody was trying to get it out. When I saw that it got cut and was bleeding, I just cried and cried and cried.