Leonard himself tells us that memory is unreliable and Nolan made sure to keep that evident in the details of the film. Scroll down to the video if you just want the Easter egg, but this site also offers some explanation as well.
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Speaking of misremembering things, Teddy's license plate switches between SG13 7IU and SG13 71U. When Leonard writes down the number it's hard to tell whether he uses an "I" or a "1," but the tattoo definitely has a "1'"(even though Leonard says "I" when reading it). When Natalie gives him Teddy's registration, it's an "I." As for the car itself, click and see.
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Jimmy Grantz sort of shares a name from a patient in Oliver Sacks' book, The Man Who Mistook his Wife for a Hat. In the second chapter, "The Lost Mariner," Sacks describes a man with anterograde amnesia named Jimmie G. Scroll down to that chapter and read all about Jimmie for yourself.
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While the initial sequence of the film is shown in reverse, all of the sounds (except for Teddy's "No!" are played forward. Nolan wanted a very physical, real feeling scene for us to identify with, and since we never hear sounds happening backward, Teddy screaming "On!" would make it harder to immerse viewers in the scene.
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