Horror, Humor & Other Moods

Managing the Game Feel
Feeling in a game can refer to a number of fuzzy concepts. Emotion players experience at the game table is the topic of this post. Fear is an innate emotion, as is humor. Smiling and laughter are outward expressions of one finding something humorous. Outward expressions of fear may vary from becoming wide-eyed and pale, to sweating and shaking. While one frequently observes laughter at the game table, it is less common to observe anyone pale with fear or visibly shaking (thankfully). Some emotions are easily produced in a "safe" setting like the gaming table and others are not.
Part of the goal of the referee is to set a mood during a segment of the game session.  Awe and wonder, surprise, puzzlement, suspense, frustration, indignity and even anger are not too difficult to achieve and may be appropriate emotional states during immersive roleplay. The idea of any good fiction is to suspend disbelief. When we read or watch film, we are aware of being seated in a comfortable, safe environment, even though in our mind we may be far away, being tossed about on the stormy ocean, or dreadfully thirsty in a hot desert. We may be witnessing the tenderness of love or than violence and anger of war. We may chuckle when the deserving fellow takes a pie to the eye, or feel slightly afraid for a well-liked character who is in immediate danger of death. All this is possible within the context of roleplaying as well.
Like an author or director, the referee may desire to "set the mood" for a particular encounter during the game in order for everyone to enjoy it to the fullest. Some of the same tools that are used by authors and directors are also at the referee's command. Choice of vocabulary and pace of action, in other words, the power of words and language to "create" is available to the referee. Like the director, lighting, music, visuals and sound can be somewhat controlled by the referee depending on available resources. Even temperature and odor can be manipulated by an enterprising referee, giving the referee tools that neither the author nor director of film usually has available.
Some emotions are generally thought of as enjoyable or positive such as humor, suspense and wonder. We like to laugh and be introduced to new pleasures. Surprise can accompany fright or wonder and can therefore go either way towards being enjoyable or not. Fear and anger are tricky to manage and often accompany one another. Frustration is only acceptable in a game if it is very mild and short-lived. "Coming back to reality" should bring the players out of any temporary emotional state they experience through their characters. Fortunately this is usually easily done. In fact, generally it is harder to keep interruptions from spoiling a mood at the table.
Humor is an enjoyable emotion and forms a part of many entertainments. It is fairly easy to set-up a humorous situation during a game. Also, humor is often the by-product of friends joking and may occur whether planned or not. It's one of the nice benefits of socializing. Humor and horror are often mixed in film and other media as many people find the tension of horror and relief of humor to compliment each other nicely. In-game fear and horror are somewhat difficult to achieve and easily dismissed by any distraction or break in the mood. It would be inappropriate for a game or any other pass-time to place anyone in any real danger, so the only tool available for the referee is to place some fear for the fate of a fictional character into the player's mind who feels some attachment to said character and is therefore invested in the fiction of the character's predicament.
Managing one's audience, much like any live entertainer, is one of the referee's essential skills. Building suspense, interjecting humor (while avoiding silliness), and affording players a sense of being immersed in a story is both exciting and rewarding work. It is also a skill that develops over time for most of us. Practice seems to be the best way to mastery of these referee skills, but they do transfer across genre and system and even outside roleplaying altogether. A good referee is probably a good teacher and entertainer as well. Someone who can hold an audience's attention and paint a mental picture with words can use this talent in many ways.