yes and no? not shown though and not gorey. SPOILER WARNING :
The dog is in a crate in front of the mirror, after a while of waiting and whimpering under the sheet the dog disappears.
SPOILER WARNING!!! The main character tells you the story of the mirror, which has supposedly killed/eaten/gotten rid of multiple dogs and cats. The main character also has a dog in a cage in front of the mirror throughout the film. No animal is killed on screen though.
The dog is in a crate in front of the mirror, after a while of waiting and whimpering under the sheet the dog disappears.