Original: Sled dogs , known also as sleighman dogs , sledge dogs , or sleddogs , are highly trained types of dogs that are used to pull a dog sled , a wheel-less vehicle on runners also called a sled or sleigh , over snow or ice , by means of harnesses and lines .
Simplified: Sled dogs are expected to demonstrate two major qualities in their work ( apart from basic physical capability to pull the sled ) .