Continuity mistake: Harry Palmer uses the leather wrist restraints to lacerate his wrists - the pain enables him to resist being involuntarily hypnotised. The next time he is woken roughly by the guards for another hypnosis session, his wrists are unmarked.
Continuity mistake: While a prisoner, he grows a stubble. Upon escaping in the telephone booth, he is clean-shaven, but subsequently regains his stubble.
Continuity mistake: When Palmer comes home and finds the dead American agent on the floor in his flat, the dead agent's eyes and mouth are both wide open. There is a cut to Palmer standing in a door-way, then a cut back to the dead agent, whose eyes are now half-closed and his mouth completely closed.