Sniffing each other's hind ends is a common way for dogs to greet. A number of other mammals also inspect each other by sniffing---but what exactly does this behavior tell the animals? A neuroscientist recently put rats to the test and found that sniffing each other actually reinforces the rats' social hierarchy, poentially staving off conflict.

The researcher put sensors in rats' noses to measure the frequency of their sniffs and mounted wireless transmitters on their heads so he could record the data. Then the researcher paired up the rats to see how they interacted. After an initial burst of mutual, exploratory sniffing, the rats would end up face to face, with one rat sniffing more than the other. The neuroscientist had an inkling that the behavior was a form of social communication, so he paired rats up based on known social hierarchies: large males with small males, and males with females. In both cases the dominant rats (large, male) ended up sniffing more than the others (small, female). In response to being sniffed, most lower-rung rats slowed the rate of their sniffing. The researcher took this to be a sort of retreat, because if the lower status rat didn't slow its sniffing soon enough, the dominant rat would respond with aggressive behavior. The researcher double-checked his hypothesis by chemically turning off the rats' ability to smell. The rats higher up the social ladder sniffed just as frequently as before, even though they couldn't smell anything, and the lower status rats still slowed their sniffing. Taking a whiff, then, is as much about conveying information as collecting it. It reinforces rats' places in the social order. These findings

, published today in Current Biology, offer a new view of how animals communicate through social behavior. Image courtesy of siamionau pavel/Shutterstock