In The Raiders Minimization (2013), Sheldon mocked Amy's favorite show Little House on the Prairie (1974) because of several anachronisms in it (such as peanut butter and telephones that wouldn't have been there in the late 19th century), saying that if he knew the show was about time travel, he would have watched it sooner. This remark may have inspired Amy to write her own Little House fan-fiction featuring a time traveler.
First episode featuring Leonard and Sheldon's 'superfluid theory' which is periodically revisited over the remaining course of the series.