put (someone or something) out of its/(one's) misery
1. To kill someone or something as a means to ending suffering. Considering the dog's extensive wounds, the vet encouraged us to put him out of his misery.
2. To quell one's curiosity. Oh, just put me out of my misery and tell me how the movie ends!
put some creature out of its misery
to kill an animal in a humane manner. (See also put one out of one's misery.) The vet put that dog with cancer out of its misery. Please, put my sick goldfish out of its misery.