When polar bears are angry, they hiss like cats.

They also growl, chomp their teeth, and snort. Polar bear cubs also hiss and cry for various reasons.

Legend has it that polar bears cover their black noses to better camouflage themselves in the white snow, but scientists who have observed polar Bear behavior have never seen this.

Furthermore, polar bears are not left-handed (or left-pawed). They use their left and right paws equally.

Another cool fact: As you can see in the picture, sometimes polar bears play with dogs. More pictures here!
(Sources: 1, 2)