In humans, each eye has a small blind spot corresponding to the point where the optic nerve leaves the retina. Normally this isn’t noticeable because the brain can fill in the gap with information from the other eye. But by closing one eye and positioning the target at the appropriate angle, it’s possible to invoke the gap deliberately.

“When the famous physiological psychologist Karl S. Lashley was forced to endure an irritating dinner guest, he amused himself by bringing his blind spot over the person’s head, neatly decapitating the person.”

— Jearl Walker, The Flying Circus of Physics, 2006