Ghost pet

Pets, like Sims, leave ghosts after they die.

The Sims: Unleashed
In the original sims series, there was no death of old age (since sims were practically immortal), but sims can die of other, more unnatural deaths. So in The Sims: Unleashed, there was also no death of old age for dogs and cats, but they could die. Unlike later games, Pets could die in a fire and of starvation. When a dog or cat dies, thier gravestones will be different from "human" sims, and thier ghosts will appear occasionally, but thier is no difference in ghost colour depending on thier death.

The Sims 2: Pets
In The Sims 2: Pets, dogs and cats can only die of old age, and their ghosts are white. More often than not, a Sim may spot a beloved pet floating around the house at odd hours, though the Prima Guide for The Sims 2: Pets states that ghost pets will only interact with other ghosts. If University is installed, a pet can be brought back to life with the Resurrect-O-Nomitron.

Ghost dogs will dig ghostly holes.

The Sims 3: Pets
right|300px In The Sims 3: Pets, pets can only die of old age, and ghost pets can be brought back to life just like all other ghosts.

Ghost Dogs

 * Can dig holes
 * Can still build relationships with Sims
 * Sims with the Dog Person trait may get the Moodlet to see their dog's ghost

Ghost Cats

 * Can still hunt
 * Still can build relationships with Sims
 * Can interact with other animals
 * Sims with the Cat Person trait may get the Moodlet to see their cat's ghost

Ghost Horses

 * Can be ridden
 * Still has saddle when they die
 * Sims with the Equestrian trait may get a Moodlet to see their horse's ghost