Understanding Dog Language

The following are some signs that indicate what a dog is feeling or saying and helps you understand dog language...
Eyes: When a dogs eyes are wide open, looking straight at something or someone and his pupils are dilated it indicates fear. When a dog fixes his eyes on something it means he is challenging you. Never look straight into the dog's eyes unless you want to challenge him.
Nose and mouth: When the dog shows his teeth he is in an aggressive state. If his tongue is hanging out of his mouth, he is relaxed.
Ears: When a dog puts his ears back it means submission or fear. If the dog's ears are erected forward, it means alert.
Tail: When a dog wags his tail it indicates desire to relate or provoke another. It is not necessarily a sign of friendship or happiness.
If his tail is erect and not moving it means he is trying to dominate.
When it is low but not hanging, the dog is relaxed. If it is hanging, curved or under his behind, the dog is showing submission or fear.

Questions and answers
Q: I have a bull terrier Skipper, that is very friendly, but whenever he sees another dog he lifts his tail and goes running toward the dog. When he does this, the other dogs usually get aggressive. What are they doing?
A: It sounds like Skipper is not as friendly as you think him to be. When a dog advances toward another with his tail up it can indicate challenge.
On the other hand the facial expressions that bull terriers have can sometimes be misinterpreted by other breeds because their eyes can sometimes give the impression that they are staring directly into the eyes of the other dog.