Sledge Dog. Photo From Life.

When following the trail much confidence is vested in the leader and should perchance it strike a blind or cross trail, it will howl to attract the attention of the driver and by these means verify directions, as if to ask if it is leading right. In case it loses the track it will slow up, whine, run up or criss-cross its tracks, sniffing and smelling in an anxious, expectant way, until it finds or is led correct, when it howls with delight and pulls off "like blazes" again.

Source: Dogs Manual