It's a Noodle Incident. Maybe she was born with one leg, maybe she got sick, maybe she got into an accident, only Greg Miller knows.
In "PU to P.E." Why didn't Mr. Workout the gym teacher and the students ever stop and think what would happen if a machine was exposed to water? Are they too stupid to realize that Robot Jones is a machine and getting him wet is ill-advised?
In "Jealousy", why is there a keyhole inside Robot's heart and what is its function?
How did Robot and Socks first meet?
How did Socks get his nickname?
What happened to Finkman?
Where are Lenny and Denny's parents?
Mr. Mitchell wasn't able to fix the broken Scantron machine in "Scantron Love".