"Maintaining a high body temperature also takes energy. Sloths reduce this cost by maintaining a lower average body temperature than other mammals. Dogs, cats, horses, sheep, rabbits, pigs, and cows all have average body temperatures between 100 and 103�F, but a sloth's average body temperature is 93�F.

Just as important, a sloth's body temperature fluctuates with the ambient temperature. Like snakes, frogs, and other "cold-blooded" creatures, a sloth's body temperature is highest on warm, sunny days, and lowest at night and on rainy days. Sometimes a sloth sunbathes in the morning to warm up. Then, during the hottest part of the day, it hides in the shade so it won't overheat. During a 24-hour period, a sloth's body temperature may vary as much as 10�F. If the body temperature of a person, a dog, or a cow varies just 5�F, it can be life threatening."

http://nationalzoo.si.edu/Publications/ZooGoer/2004/6/sloths.c fm

It seems almost like sloths are just constantly expecting this to happen. I have an extremely difficult time believing they are ever surprised with anything.

Can you imagine how nasty a sloth must taste?