When trying to analyze an animal's body language, each signal must be taken in context. Other body language signals should be analyzed as well to form as complete as possible view of the animal's intent or emotional state. You can generally characterize signs in 3 categories: go, stop and yield. 

​Body blocking is a body language cue which is intended to stop the motion of another animal. This is often very subtle and may just look like the cat is resting. It is a STOP signal. 

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 The calico cat at the top of the stairs is blocking the access of the cat at the bottom of the stairs to the upper level of the house. She is also making direct eye contact. The other cat is averting her gaze.

The cat in this photo is blocking the access of the puppy to the doorway leading to the rest of the house. He is also making direct eye contact with the puppy to further stop his forward motion.