Fear and fear tests
Fear will play a major part in the game, but the fear rules in the basic book leave something to be desired (seriously, you stand a pretty good chance of getting major psychological hindrances or even death with a failure). So I kind of cut things down to something a bit more simplified.
A Spirit check failure means the character is afraid. The character is considered ‘Shatnered’ at that point, being able to move but unable to act, until a fear test is passed. The player is encouraged to come up with some sort of fearful response for their character (running away, standing in place and gibbering to oneself, maybe trying to hide behind other characters, dropping what they’re carrying, etc). Hysterical actions may be allowed, if they’re funny enough at the time (blazing away with full auto weapons blindly, throwing a grenade without pulling a pin, maybe pushing another person between you and what’s got you scared, slamming a door shut, etc), but should not always be expected to be the norm.
A critical failure on the Spirit check (rolling a 1 on the Spirit dice and the hero dice) means the character is automatically shaken for that round only. They are able to reroll the fear test and accept the actions on each following round.