Cheetahs may be the world's fastest land animal, but they give up about 60% of their chases. In 1973, researchers thought they had figured out why. When they put the big cats on a treadmill, the animals stopped running after their body overheated, reaching temperatures of 40.5°C. But scientists wanted to know what happened in a real hunt, so they implanted temperature and movement sensors into six roaming cheetahs (Acinonyx jubatus, pictured) in central Namibia and tracked their body temperature and activity for 7 months. (Two were killed by leopards during the study.) A cheetah's body temperature does not significantly rise during the chase, but increases on average 1.3°C after a successful hunt and 0.5°C after an unsuccessful one, researchers report online today in Biology Letters. The team speculates that this temperature spike could be stress-related as the cheetahs keep on the lookout for more dominant predators such as lions and leopards looking to snatch their dinner. Still, no one knows why the quick cats throw in the towel on most of their chases.