A dream in which you see someone else kill a dog symbolizes feelings of loneliness. Dogs in the dream stand for friendship and seeing one get killed means there might be issues to do with your social life, friendship, or relationship.
There are other meanings depending on the details of the dream.
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There is a friend that is not happy with you
Seeing someone kill a dog in the dream could mean there is someone in your circle of friends that is unhappy with you for some reason. The dog, as a symbol of friendship, was killed as a manifestation of the wedge building up between you and your friend. It is up to you to identify this friendship to see if it’s worth saving.
A part of your life might soon be exposed
Dogs in the dream can also be symbols of guarded secrets. Seeing someone kill a dog could therefore mean something you would not like revealed might soon be exposed. It might be something big and devastating, or something trivial and only slightly embarrassing.
You will need to act with courage soon
To see someone kill a dog in the dream symbolizes a need for you to act with courage. The dream means something could soon happen that will require you to cast any cowardice aside, a trait that is sometimes symbolized by dogs in dreams.
Dream about someone killing your puppy
Seeing someone kill a puppy means there is a budding friendship that you are having second thoughts about because of the opinions of those around you. This has nothing to do with whether the friendship is good or bad. It simply means people around you might not have much good to say about the other person.
Dream about someone killing an attacking dog
A dream in which you see someone kill an attacking dog means there is someone malicious within your circle of friends. This is an enemy that hides behind a mask of friendship and soon, their true nature might be revealed. The dream could be considered a call for you to look at your life and get rid of all those that might seem fake.
Dream about someone killing a brown dog
A dream in which someone kills a brown dog means there might soon be some friction within your circle of friends that will leave you feeling ungrounded. In other words, this is some kind of conflict that will knock you off your feet. The dog itself stands for friendship while its brown color stands for the earth and the idea of being grounded or having your feet on the ground.