The cutscene override is a trick that allows Jim to continue moving while a cutscene or dialogue plays. In order to activate a cutscene override, press L to open the Morph Powers menu at the moment you trigger the cutscene; this is usually the moment when you first step on the "tile" where the trigger is. A side effect of cutscene overriding is that, while the cutscene is overridden, any enemies in the room will be frozen in place.

NOTE: If the cutscene is triggered by pushing a crate onto a pressure plate, you must also switch the active Morph Power (with B or A) for the cutscene to be successfully overridden.