Communication
Guinea pigs have a variety of different ways of communicating using body language. Here are a few of the behaviors you may see from your small pet:

Jumping: Guinea pigs leap up in the air when they are happy. When a guinea pig jumps straight up in the air, it’s called “popcorning.”
Nose Touching:When a guinea pig touches the nose of another guinea pig, pet or favorite human, it is a way of saying hello.
 
Playing Dead: In the wild, cavies lie motionless on their backs to make predators think they are already dead. Domestic guinea pigs sometimes use this tactic if they become very frightened. If you see a guinea pig playing dead, remove whatever is scaring it (usually a stranger or another animal), and pet it to reassure that everything is OK.
 
Stretching: When a guinea pig lies down and stretches its body out, it is feeling very safe and relaxed. 

Stiffened Legs: Rising up on stiffened hind legs is a defensive movement usually reserved for other guinea pigs and is meant to warn off intruders. If the other guinea pig ignores this symbol and fails to retreat, a fight may ensue.

Scent Marking
Guinea pigs also mark their territory using scent. A guinea pig will rub its chin on objects around its cage or the room, or possibly even you. It may even rub its rear end along the floor. This is its way of letting other guinea pigs know that whatever object is being marked belongs to it. (A guinea pig may do this even if no other guinea pigs are around.)

Signs Of Stress
When a guinea pig is stressed out, it may sleep more, spend a lot of time hiding in its cage or not eat very much. If you see a guinea pig displaying these signs, evaluate its living situation and think about what might be causing it stress. A noisy environment, too much handling by strangers and the presence of a cat or dog are some things that can cause a guinea pig to become stressed.