Revealing mistake: The phone message that Ryan leaves on Luke's voicemail is different to what he originally said, which is "I want to make sure you took care of it. Take care of it," but the message recorded is, "I'm just calling to make sure you took care of it. Take care of it." Also the background sounds from the club - the music, people talking, etc, are missing.
The Escape - S1-E7
Revealing mistake: Just as Jimmy is about to kiss Kirsten, you can see the actress nod to signal him, which wouldn't be right as in the story Kirsten doesn't want to kiss Jimmy.
Revealing mistake: The picture of Marissa and Ryan that Oliver hides is from the pilot episode, at the fashion show hosted by Marissa. However, at the time she and Ryan barely knew each other and wouldn't have an excuse to take a photo together.
Revealing mistake: If you look closely, a bit into the fight you can see that Hailey is not actually putting any trash inside the trash bag. She is just going through the motions.
The Case of the Franks - S4-E13
Revealing mistake: When the limo pulls up to the hot dog stand, Julie steps out from the back seat. And as she walks toward Frank standing in front of the picnic tables, the limo driver is visible behind the wheel. Julie joins Frank at a table, and then Ryan decides to enjoy a last spin in the limo telling Taylor they've rented it for 2 more hours. In the next shot they are sitting in the front seat talking while Ryan is at the wheel, when the limo driver never left the vehicle. (00:41:20 - 00:42:46)
Answer: Hallelujah by Jeff Buckley.
Bobbert