Savage: someone who is rude, impolite.

Couch down: bend the legs and close to the ground.

Bristle: if an animal is frightened or angry, his fur will stand up.

Swerve: Change the direction suddenly.

Trembling: Sharking. To be very frighten.

There are lots of dogs in the countryside. If you meet a savage, he might bark you with fur bristled. Please don't be threatened even your legs are trembling. Then crouch down for few minutes, he will swerve.