 SPOILER: The scene in which Kirk stumbles into his chair after  hearing of the death of his son was an improvisation by  William Shatner (qv), who was told by Leonard Nimoy (qv) to do  whatever reaction Shatner wanted to do. Shatner has never told  whether he meant to miss the chair and slip to the ground, or if he  had meant to simply hit the seat hard but missed going backwards.