It's nearly Halloween, the time of year when no one could blame you for believing in ghosts. These otherworldly spirits bring to mind elusive shapes, pale colors, and strange sounds.

And some wild animals with these very same traits have an equally spooky reputation. (Read "How Cats, Rats, Bats, and More Became Halloween Animals.")

For instance, lemurs of Madagascar make haunting territorial calls that once reminded people of "ghosts or spirits living in the forest,” says Chelsea Feast, lemur expert for the Tennessee Aquarium. The word “lemur” comes from the Latin word for ghost. (Listen to some lemur sounds.)

Black and white ruffed and red ruffed lemurs, both critically endangered, make calls that