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Partway through season 2, Kiefer Sutherland injured his leg while exiting his trailer, so a small scene was written in where Jack Bauer must pull a piece of shrapnel from his leg after a plane crash to explain Sutherland's limp.

All cast members were required to have their hair trimmed every five days.

In season 3, it's revealed that Jack received an intricate tattoo on the inside of his left forearm as part of his previous deep-cover operation with the Salazar brothers. Instead of spending hours in the makeup chair on days when the tattoo needed to be shown, Kiefer Sutherland opted instead simply to get the actual tattoo.