What does it mean when a dog raises one leg and looks ahead intently? This is a very specific form of canine behaviour in my opinion. You will find answers which are quite variable because they are describing less specific forms of dog behaviour. In this instance I’m referring to a dog picking up their foreleg and then leaning forward with an intent gaze into the distance as they detect scent.
There are other circumstances when a dog may raise their foreleg such as when sitting on the ground simultaneously. I’m not referring to that example a body language. The picture on this page illustrates what I’m referring to.
This instinctive body language is part of a hunting sequence. It is seen in dogs like the English Pointer which is specifically trained to work with people who are hunting. It is an adaption of normal canine behaviour. When a dog is tracking their prey they pick up their scent. When they do this they point their noses towards the source of the scent, straighten their back and stretch out their tail while lifting their front leg. I guess that you would see it in the park if your dog has a propensity to chase squirrels (which I disapprove of).
This gives me the opportunity to briefly refer to the Pointer; a specialised breed of gundog that hunts by scent. When they detect prey they freeze and adopt their characteristic “pointing” posture. The head is lowered and the neck stretched forward. The tail sticks out stiffly behind in a horizontal position. One of his front feet is held up as if frozen in mid-step. The dog stands till like a statue and he may hold his position for a long time. There may be a slight trembling or quivering especially of the tail. This indicates excitement and some tension in the moment. It is reported that one dog kept up this position for several hours. When hunting with a person, the position is broken when the person fires at the prey.
The Pointer has inherited the behaviour of their canine ancestor the wolf. When wolves first pick up the scent of prey the leading members of the pack stop in their tracks and point themselves in the direction of the scent. Other members of the pack then follow trying to catch the smell themselves. There is a pause while all members of the pack pick up the smell whereupon they begin the next phase of their hunting operation. In the Pointer’s behaviour the pause is longer than happens naturally by the wolf. This is a result of selective breeding of this dog breed.