The "ear" was grown on the mouses back because it's a good idea to have a "spare" human ear. The ear is very difficult to repair and is often damaged in car accidents, fights, fires, and also a disease called microtia; meaning "little ear" which can result in a slightly smaller ear or almost no ear. Also because it is mostly made of cartilage, which is hard to work with and the ear has a complicated shape that is highly visable.
Growing an ear on a mouse involves a process called tissue engineering, where a biodegradable scaffold in the shape of an ear is implanted under the skin of the mouse. Cells taken from the mouse's own body or from another source, such as a 3D printer, are then added to the scaffold where they grow and form the ear shape. The scaffold eventually biodegrades, leaving behind a functional, biological ear on the mouse.
Usually when a mouse ear gets crusty its because it has an ear infection or a tick (flea)
go to the vet and get the ear stiched.
The number varies by about seventeen.
A human ear
snake
You should have had it done by an professional body piercer, not some clown in the mall, go see your doctor.
About six inches.
stirrup
When they are grown up and when they are over 4inches.
ear force one
It took about several months