Upside down and can't throw up

摘要

A sloth can't vomit. It has a one-way throat, handy for eating while dangling upside down by the toes. But the animal has to be careful not to poison itself by nibbling too many toxic leaves that it can't easily purge. There are upsides and downsides to evolving a body that can hang toes-up for some four to six hours a day, as the three-fingered sloth does, says sloth biologist Rebecca Cliffe of the Sloth Sanctuary of Costa Rica near Limon.