Continuity mistake: After Jack brings the puppy over to the girls, the box he brought the puppy in was placed on the back end of their couch. At one point, it is knocked over, and you can see it falling down to the floor (past Janet). In a few shots, it's back on the table, and none of the characters were in a position to pick it up to place it back there.
Continuity mistake: Larry gives Cindy and Janet gifts to thank them for letting him live with them, so Janet gives him a kiss. However, three seasons later in the episode "Friends and Lovers," Janet kisses Larry at her wedding to which Larry says "Janet, that's the first time you've ever kissed me."
Trivia: In the episode where Janet asks Jack if she's a bad kisser, take a look at Janet when he kisses her. Jack unexpectedly slip Janet his tongue (which surprises the audience as well) and that throws Janet off and shocks her. Her surprised face is not acting, and was really surprised he did that. You'll also notice that when they part, she can't keep a straight face.
Trivia: Of all 5 roommates (Jack, Janet, Chrissy, Cindy, Terri), the only parent of a roommate never to appear in any episode is Cindy's mother.
Chrissy: Jack, that smells good.
Jack Tripper: Chrissy, I haven't even started cooking yet.
Chrissy: Well, you better hurry up and start cooking so you can catch up with the smell.
Diane McMillan: Janet, do you know what I do for a living?
Janet Wood Dawson: Of course I do! It's right here on your card in black and white. Diane McMillan, The Rapist.
Jack Tripper: That's therapist.
Janet's Father: She always did have trouble with her reading.
Jack Tripper: Larry, haven't you ever thought of telling a girl the truth?
Larry: Well, I figure, anyone who gets up an hour early to put on eyeliner, fake eyelashes, and plastic nails isn't someone who wants to hear the truth.