Phantom limb

This man is experiencing the phantom limb phenomenon. By placing his intact hand in front of a mirror and the amputated hand beside it, the reflection of his intact hand will actually be felt like the hand of his amputated hand. This is because of dendrites in his amputated hand still signal the missing part and "thinking" that it's still there.

Phantom limb: the illusion that a limb still exists after it has been amputated