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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.

The actors are not told in advance as to what will happen from episode to episode so none of them know whether or not they will be written out of the series

During season two shooting, Elisha Cuthbert was bitten by the mountain lion who menaced her in one of the plotlines. Before shooting the scene the animal trainer suggested she "meet" the mountain lion before shooting, when she went to pet the mountain lion it bit her hand. She was taken to the hospital, treated for puncture wounds and was given a tetanus shot.