Notice the eyes. Does his glance linger a bit longer than is socially acceptable, or does he watch you from afar? Maybe he looks at you, looks away and quickly glances at you again, or perhaps his eyes light up when he's speaking to you. All of these moves signal interest and passion.
Listen for frequent use of your name. If she repeats your name several times during the conversation, it's a clear sign of attraction. People tend to repeat the name of someone they like much more often than they do with those who repel them.
Measure your personal space. Don't do this literally, of course, but take notice of how closely he stands to you when you're speaking to each other and how closely he sits to you on the couch. When he invades your personal space as if he's drawn to you and leans in during a conversation, it's a clear sign of attraction.
Watch and see if she lifts her shoulders. Lifted shoulders are an indication of attraction. According to David Givens, Ph.D., this is what's called the "cute response" and reveals softness and compliance. Look into her eyes while you're speaking to her, but keep an eye on those shoulders as well.
Watch his palms. Dr. Givens states that when a person exposes one or both palms to you, it's a sign of vulnerability and openness. Resting his hand on a table or his leg, palm upward, is a sign that he could have feelings for you.
Notice her gestures. Does she caress her arm, hand, thigh or other body parts while you're talking to her? Does she play with her hair, a straw or a pencil while you're conversing? She may be subconsciously expressing a desire to touch you, or be touched by you, in the same manner.