He is exploiting his audience's "change blindness".
Change blindness refers to a perceptual phenomenon that happens when an adjustment in a visual improvement is presented and the eyewitness does not see it. For instance, observers frequently neglect to see real contrasts brought into a picture while it flashes now and again again. People's poor capacity to identify changes has been contended to reflect crucial confinements of human consideration. Change visual impairment has turned into a profoundly investigated theme and some have contended that it might have imperative down to earth suggestions in regions, for example, observer declaration and diversions while driving.