The first indication of this unusual behaviour is usually witnessed when the dog jumps on a shadow on the floor and then the dog tries to either dig at it or chase it with it's front paws. Sometimes they try to bite at the shadow it as it moves . Children using a torch or laser beam as a fun game with the dog, can trigger the 'chase' behaviour. Much laughter follows as the dog tries to 'catch' the light and this rewards the dog for performing this behaviour..
In some dogs this starts what can actually becomes an obsession and the dog becomes 'addicted' to try and find shadows to 'chase'. This leads to a dog who cannot rest normally and spends much of his time hunting for shadows to 'chase'.
Tail chasing begins in much the same way . Watching your puppy chase his tail is often accompanied by much laughter and hilarity as children watch their new puppy spin around and try and catch it's own tail. This behaviour too can become an obsession or an addictive attention seeking behaviour. The best approach to prevent this happening is usually to ignore such behaviour when you first see it or I often suggest that you leave the room when it happens. The consequence of you leaving the room is a good approach as it prevents you reinforcing the behaviour by any verbal, or visual communication that would result in the dog wanting to perform this behaviour again..
So, it is a practice to never tease your dogs with lights, laser pointers , reflections or shadows
Sometimes this behaviour can indicate in dogs a serious behavioural problem.. If you have constantly ignored your dog's light or shadow chasing and it has not resulted in an improvement of the behaviour please contact your Vet who can refer you to a Behaviour Counsellor .. Also if your dog is chasing 'imaginary flies or starting into space these both are behaviours that require professional help.