"I Know What You Did Last Summer" is the ninth episode of season four of TV series Supernatural and the sixty-ninth episode of the series overall. It was directed by Charles Beeson and written by producer Sera Gamble. It premiered on the CW Network on Thursday, November 13th, 2008. In this episode, Sam and Dean must team up with Ruby to find Anna, a girl who can listen in on angelic conversations... and who the demons want to acquire. Ruby seemingly betrays the Winchesters and takes off with Anna. Meanwhile, Sam fills Dean in on how he met Ruby during Dean's time in Hell.
This episode was watched by 2.94 million viewers. 
Coincidentally, this episode first aired exactly ten years to the day after the theatrical release of I Still Know What You Did Last Summer. I Still Know What You Did Last Summer was released on November 13th, 1998 in the United States.
The title of this episode is taken from the 1973 Young Adult novel I Know What You Did Last Summer by Lois Duncan. The book was loosely adapted into a feature film in 1997 by Jim Gillespie, also called I Know What You Did Last Summer. The episode itself pokes fun at the film moreso than the novel.
Dean makes a reference to the 1999 film Girl, Interrupted starring Winona Ryder and Angelina Jolie.
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