"Penile fracture," as Mark suffers, can (very rarely) happen when an erect penis encounters unusual force. What "breaks" -- or rather tears -- is the tissue that creates the erection.
Denny asks Izzie if she believes in Heaven. In the season 2 episode "Into You Like a Train", Bonnie asked that of Tom (they were the people impaled on a metal pole). Weirdly enough, in the season 3 episode "Some Kind of Miracle", Denny and Bonnie knew each other in Meredith's afterlife.
Denny first says that he's here for Izzie in the episode These Ties That Bind. Izzie finally figures out what he means by that in this episode. He also says it in a couple of other episodes leading up to this one.
It's revealed that Lexie is 24 years old.
It was Izzie's birthday in this episode. So that suggests that her birthday is on Jan 8th.
Goof: During the scene where Cristina choose Alex for the solo surgery, she writes "Karev, A" on the OR board in the middle of the box. But later on in the scene when Meredith walks up next to Derek, the board says only "Karev" and it is higher up in the box.
The little girl was watching Phantom of the Opera on the TV in her room.
Goof: Dr. Virginia Dixon tells Bailey that the first successful heart transplant was performed in 1896 by Dr. Ludwig Rehn, which is a very serious mistake - in 1896 Dr. Ludwig Rehn actually performed a very first successful heart surgery in recorded history, but not a heart transplant. First cardiac transplantation was performed only in 1967 by Dr. Christiaan Barnard in South Africa. It's hard to believe that Dr. Dixon would make such a mistake in her area of expertise.
Goof: In the first parts of the episode, Izzie is wearing a long-sleeved red shirt beneath her hospital clothes, but, in the end, when she is about to change, you can see that she doesn't have it anymore.
Jeffrey Dean Morgan (Denny Duquette) although appearing throughout the entire episode, only says the last five words "Are you sure you're okay?"
At approximately 31mins, Sloan and Torres are in bed together. When Shepherd comes in, Torres completely hides her head and arms under the cover. After some brief talking, Shepherd leaves, and now only her head is covered and her arms are completely visible.
When Meredith starts reading her mother's diary the date on the first page is Oct. 13, 1977.
Goof: When George is showing Dustin the video camera in the OR, he twists it back and forth, so that the picture on the monitor moves too. When the shot cuts away from the OR monitor, the image of Dustin is at an angle. In the next shot, the image is at a completely different angle, even though George let go of the camera.
At the end of the episode you can see a "Dermatology" sign on the door of trailer. It looks like an actual Derm sign that one of them stole perhaps, as opposed to a simple sign with the word "Dermatology" written on it.
Cristina's phone is a red Blackberry pearl, 8130 series.
Throughout the episode Dr. Walter Tapley repeatedly refers to George as O'Leary.
The Chief's phone is a Blackberry Curve 8000 series.
Derek's middle name is Christopher.
When inquiring about Callie's relationship with Hahn (specifically, whether or not they're a couple), Addison asks, "Are you performing in the Vagina Monologues now?" Actress Sara Ramirez, who portrays Callie, acted in The Vagina Monologues along with Tovah Feldshuh and Suzanne Bertish.