If a guy starts cracking jokes as you're waiting in line together at the supermarket, it's possible he could be attracted to you. Humor can be a way of testing the social waters, says psychology professor Norman Li in the May 2011 article, "Want to Know if Someone Likes You?" in "Psychology Today." If you laugh at his jokes, you're giving him a sign that you might be interested in return. Try the same thing yourself to get an idea of whether or not the object of your interest is on the same wavelength. For example, you might use your favorite line about how politicians and diapers both need to be changed regularly for the same reason and see how he reacts. If he's interested, it's likely he'll laugh, even if he's running for a seat in his state's legislature.

The eyes are not only windows to the soul, but to the heart, as well. One way to gauge whether the woman you've had your eye on is attracted to you is to take a close look at her eyes. When a person is attracted to another, pupil size increases. The diameter of a person's pupils "is known to have a proportional relation to the observer's level of interest," notes the November 2007 study, "Women's Pupillary Responses to Sexual Significant Others During the Hormonal Cycle," published in "Hormones and Behavior." Pupils aren't the only ocular giveaway, however, as sustained eye contact is also a clue that your interest may be reciprocated. Try looking at her from across the room and see whether or not she returns your gaze. Don't turn it into a staring contest, however, as anything more than a few seconds will appear as though you're initiating a staring contest.

To figure out if two people are attracted to one another, make like Jane Goodall and study primate body language. If attraction is present, body language will tend to be open, with arms and legs uncrossed, and feet pointing in the direction of the other person, rather than the door, says social anthropologist Jean Smith in the July 2013 article, "The Signs of Attraction -- Body Language," on her personal website. A person who finds another person attractive will sit facing that person, and may tilt her head. Smiling is another hint that someone finds another person pleasing. Give the object of your affections a broad smile and see if she returns the gesture.

If two people enjoy spending time together more than with anyone else, it's safe to say there may be a level of attraction present. A person's heart lies where he puts his time, so if he chooses to be with you rather than with his buddies, that's a sign that he may be into you. Conversely, if it's hard for a person to schedule time to see another, chances are his interest lies elsewhere. The next time he tells you that he'll have to pass on attending your party because Friday is the night he meets his rugby buddies at the pub, it's a good bet that you'd be better off focusing your attentions elsewhere.