When the mechanical men march to attack the Jupiter II, John Robinson says, "Smith take a position behind that rock; protect our right flank." However, he is directing Will and Smith to take up a position on his left flank.
The rocks that Dr. Smith lifts are obviously fake. You can clearly see the bottom right portion of the prop quivering when Smith, under the robot's personality, lifts and carries the second rock.
At one point, John asks Smith: " What can we do for you?" to which Smith responds: " As a matter of fact there is.".
At about the 24 minute mark the backs of the small robots guarding Dr. Smith are facing the camera and the "Remco" brand name and logo are visible and readable.
During the fight at the end Smith (in the robot's voice) misquotes Tennyson's poem 'The charge of the light brigade.' He quotes one line as 'Into the valley of death rode the brave five hundred' instead of 'All in the valley of death rode the six hundred.'
When the robot comes to visit the Robinsons at the weather station, wearing the crown and robes, Professor Robinson asks him "what can we do for you?" the robot answers in Dr. Smith's voice "As a matter of fact there is" - as if the question were "is there something we can do for you?"