What is the smallest mammal pet?

The smallest mammal pet I've ever seen in real life so far (none of those exotic tiny marmoset monkeys!) was a baby sugar glider that my neighbor in Malaysia had bought from a pet shop in Georgetown, Penang.
The sugar glider he had was about 6 inches long and enjoyed curling up in his pocket. It was adorable and was apparently some kind of gliding marsupial that (when it was more mature) could glide through the air from tree to tree. He fed it a mix of live crickets and mealworms and supplemented it's diet with fruit and vegetables.

I'll try to post some photos later.