Continuity mistake: In the second episode of the series Eric's Birthday is in May. The second episode of season 5 Eric says his birthday is in March. In season 6 Eric's Birthday occurs after graduation, which would make his birthday after June.
That '70s Show (1998)
1 continuity mistake in show generally
Starring: Mila Kunis, Ashton Kutcher, Topher Grace, Danny Masterson, Laura Prepon, Wilmer Valderrama
Punk Chick - S1-E22
Other mistake: Jackie and Kitty are baking a pie in the kitchen and Kelso walks in. Jackie and Kelso have an awkward encounter as if they are separated, but they got back together at prom.
Fez: Having sex with someone you work with is horrible. I don't know how Donny and Marie do it.
Trivia: In the fifth episode of the first season, Donna is left alone to babysit her little sister Tina. Both Tina and Valerie, Donna's older sister, were written off the show, much the same way as Richie's older brother Chuck, on Happy Days, or Laura's younger sister Judy, on Family Matters.
More questions & answers from That '70s Show
Answer: It's Ashton Kutcher's dog.