The dirtiest job so far? "Bat biologist has got to be near the top. Bracken Cave is home to 40 million Mexican free-tail bats. The bats are hanging overhead, urinating constantly, defecating deliberately and giving birth randomly. All of the aforementioned substances are falling upon us. The guano that we're standing in is filled with billions of flesh-eating beetles, which survive on dead bats that periodically plummet from the ceiling.

Bracken Cave is like no other place on Earth, and quite possibly the dirtiest hole on the planet."