A confident, happy dog stands straight and tall with its tail out and wagging or relaxed. Its head is up, its ears are relaxed and you will probably only be able to see the colored parts of its eyes.
When a dog is scared, however, it gets ready to run or fight, so its posture changes. A dog crouches to lower its stance and tucks its tail between its legs. Its ears either flatten back against its head or stiffen so they are pointed up. It might widen its eyes so that the whites are showing. A dog might also not make direct eye contact once it is scared.