For three years, German scientists tried to coax a sloth [wiki] into moving up and down a pole for a scientific experiment:
The sloth, named Mats, was remanded to a zoo after consistently refusing to climb up and then back down a pole, as part of an experiment conducted by scientists at the University of Jena's Institute of Systematic Zoology and Evolutionary Biology.
Neither pounds of cucumbers nor plates of homemade spaghetti were appetizing enough to make Mats move.
"Mats obviously wanted absolutely nothing to do with furthering science," said Axel Burchardt, a university spokesman.
The scientists finally gave up and place Mats in a zoo, where is is very comfortable now: Link - via Clive Thompson's Collision Detection
Quoting from "The Life of Pi" by Yann Martel:
"The three-toed sloth is not well informed about the outside world. On a scale of 2 to 10, where 2 represents unusual dullness and 10 extreme acuity, Beebe (1926) gave the sloth’s senses of taste, touch, sight and hearing a rating of 2, and its sense of smell a rating of 3. [...] As for hearing, the sloth is not so much deaf as uninterested in sound. Beebe reported that firing guns next to sleeping or feeding sloths elicited little reaction."