Posted by: @sara

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Dogs mourn and grieve. They are like the second humans that have emotions. Dogs show their grieve of their lost ones by rejecting their food, playing and also being dull until that mourning period passed 

It is the same way human beings mourn for their dead loved ones is the same way animals do the same thing for their own. It even goes to the extent of animals mourning the loss of their owner because they have been so much attached to their human's that being separated from them is going to be very painful.