Slice off the skin of the eggplant. It can be tough although it is edible. You may have seen it cut zebra-striped to retain some of the fiber. You may need to use a knife. A vegetable peeler will have a tough time digging into the skin.
Cut into 1/2 to 3/4 inch thick slices.
Cut each of the slices in half to get two semicircle sections.
When the sections are stood upright, you have the profile of a mouse. You can further refine the shape by sculpting the pointy nose by cutting away some of the eggplant.
At this point, you can season and salt your eggplant. People do salt to draw out some extra moisture but I do not find it really necessary to add too much salt.
Take a good paring knife and slice down partway on the back rounded half of a semicircle when it is positioned upright.
This creates a slit to put in a piece of spaghetti for the tail.
The spaghetti strand will wedge in place on the back of the mouse.