After John and Don's attempt to rush the Robotoid results in them being violently knocked to the ground, John's hair is severely tousled. A moment later, it's back to being perfectly coiffed.
As Dr. Smith says, "The mental capabilities of this machine are unlimited," he places his hand on the semicircular rim on the Robotoid's face. As he continues, "He's simply devouring knowledge," the shot transitions from long to close, and Smith's hand is suddenly resting just above the Robotoid's arm.
The fishing poles the robot, Will and Dr. Smith are using have fairly thick white rope for a line, but when the robot catches a fish and the scene switches to the fish hooked in the water, the line is very thin, nearly invisible line.
After Will says "If I hadn't repaired that Robotoid," Smith's arms change position.
Just before the robotoid disables the robot with its laser the lower left light of the grouping of 10 on the robot's front is out. But after the robot is revived it is lit again.
Two seconds into the episode, just before Smith's first words, the camera briefly lurches leftward.
When the Robot frantically waves his arms upon first sensing the Robotoid, the on-set sound of his arms moving can be heard. When Bob May's on-set voice is overdubbed by Dick Tufeld's, the physical arm sounds cease and do not resume until after Tufeld's line "My sensors will not accept the possibility of its existence."
When the Robot finds Will after Will escapes the Robotoid, one can just barely catch sight of the dark, below-the-knee pant leg of operator Bob May in the bottom portion of the robot.
Near the end of the episode, after the Robot says, "There is much we have to discuss," the Robot proceeds to move forward, out of frame. The tow cable attached to the rear of the Robot at ground level then becomes visible (the Robot was apparently towed backwards into frame, with the motion reversed in editing).
After Don's line "[now we need to] find the alien robot," Messrs. Williams' and Hansen's marks (sticks placed on the floor) are not only visible, they're perfectly parallel to each other.
When the Robot approaches the Robotoid at night and accuses it of playing possum, Mr. Hansen is unable to prevent the Robotoid costume from visibly swaying.
During the line "Doctor Smith suffers the injury of embarrassment," one can indirectly observe Bob May's right hand activating the Robot's speech indicator (the translucent panel which lights up when he is talking). The Robot's fully-retracted right claw wiggles in sync with the indicator.
Will mistakenly calls a rheostat a "retrostat".
Will gets permission to repair the Robotoid on the basis that he could "find out where it came from and who left it here." However, in the entire post-activation portion of the episode, Will (or indeed anyone else) never queries the Robotoid about its origin or history.