As far as scientists can tell, humans are the only animals with "covert sexual signaling" (aka flirting). In many other species, males are very overt about their courtship signals, even to the extent of expensive, colorful displays. The authors of this study hypothesize that flirting is unique to humans because there are socially imposed costs to being too overt with courtship displays. Basically, in certain situations (work, for example, or in front of your crush's spouse), it could be soci
