Some people watch the competition carefully for the slightest signs of weakness. Lemurs, on the other hand, just give them a sniff. These primates from Madagascar can tell that a fellow lemur is weaker just by the natural scents they leave behind, finds a study on ring-tailed lemurs. The study reveals that getting hurt dampens a lemur’s natural aroma, and that males act more aggressively toward scents that smell ”off.”