I think you should take your dog to your veterinarian, particularly if your dog's legs only shake or tremble when he is going from standing to lying down. This could be a symptom of nerve damage or muscle weakness, which needs to be diagnosed and potentially treated before it gets worse.
Because he can!
The LITERAL meaning would be to shake one of your legs back and forth.
Male dogs can have dew claws on their front and back legs, but it varies by breed and individual. Dew claws are essentially a dog's thumb, and they are more common on the front legs than the back legs. Some dog breeds are specifically bred to have double dew claws on their back legs.
because they strain there weight
Dogs kick their back legs when they are excited as a natural instinct to release excess energy and show enthusiasm. This behavior is often seen as a way for dogs to communicate their excitement and happiness.
either the person is bored or excited about something
probably something to do with the nerves in there legs it's a age thing not an illness or anything
Dogs kick their back legs when playing to show excitement and engage in playful behavior. This action is a natural instinct that mimics hunting behavior and can also be a way for dogs to release excess energy and communicate with other dogs.
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The legs may shake if the dog is frightened.
He may be nervous or scared, or maybe he is having problems with his legs. Have him walk towards you and see if this proceeds.
Dogs have 4 legs.