Kelso tripping on the door as he was chasing Eric outside wasn't scripted. Ashton Kutcher admitted he was good at getting hurt on set often, some of which made it into episodes.
The first episode set in 1977
Hyde: "'Spy vs Spy'. Man, they kill me.".
"Spy vs. Spy" was a feature in Mad Magazine, a satirical humor magazine which began in 1952 and is still published today.