You probably shake at least a couple hands a day, but did you ever wonder what really goes into a simple “put ‘er there”?

Surprisingly, plenty of researchers have. Most recently, a group of Israeli scientists used hidden cameras to discover that men were more likely to sniff their right hands within 60 seconds of shaking with another guy.

“People don’t notice themselves doing it,” says study coauthor Idan Frumin, a researcher with Israel’s Weizmann Institute. “Even after we showed some of the subjects their videos, their initial reaction was that we had somehow doctored it.”

Why would you sniff your hand? Everyone exudes chemicals from their skin. And these chemicals rub off during a handshake, Frumin says. Even though you’re not conscious of it, your brain can pick up information about what the other person is feeling—like whether he’s nervous or happy—from sniffing his skin chemicals.

In this way, you may get a gut feeling about a guy’s emotional state even if he looks calm and collected.

Naturally, the new study prompted us to dig for more wild handshake facts. Here are six of the best.

You shake to show you’re unarmed

While a lot of history is educated guesswork, the dominant theory on handshakes is that the custom began as a way to show whoever you were greeting that you didn’t have any weapons. As you might remember from the movie Gladiator, the Roman version of a handshake involved full forearm-to-forearm elbow grabs. Historians think that may have been a way for a Roman to ensure his new pal didn’t have a dagger up his sleeve—literally.

 

A weak shake could stall your career

Hiring managers view job candidates with a firm handshake as more outgoing and capable than those with a weak grip, according to a study from the Journal of Applied Psychology. Fair or not, a firm handshake indicates self-confidence and extroversion, the authors say.

You can shake to make people like you 

Almost any human-to-human interaction goes more smoothly if people first shake hands, finds research in the Journal of Cognitive Neuroscience. By activating parts of your brain tied to social interaction, shaking people’s hands primes them to see you in a favourable light, and lowers the odds of them negatively interpreting your words or behaviour, the authors say.

You could tick some people off if you shake with your left hand

In many parts of Asia and the Middle East, people use their left hand to wipe themselves—often without the benefit of toilet paper. That means touching someone with your left hand—for example, gripping a guy’s hand in both of yours during a handshake, or touching his arm with your left hand while shaking—is a big-time offense in certain regions.

You should only shake for 2 seconds at most

While people are put off by an uncomfortably long handshake, a too-quick shake gives the impression the speedy shaker is arrogant or disinterested, finds a study from the U.K. The researchers say a handshake duration of 1 to 2 seconds is most appropriate.

You don’t have to be a psychic to read palms

At the start of a shake, offering your hand with your palm up communicates honesty and receptiveness—but also submissiveness—shows British research. While you don’t want your palm facing the ceiling, slightly tilting it open may be a good tactic when greeting a potential employer or someone who outranks you, the research suggests.

Meanwhile, extending your hand with your palm down sends the message that you’re in charge. When in doubt, just stick your hand out straight