Stripping to the waist can make a man invulnerable to bullets. A single match will be sufficient to light up a room the size of a football stadium. If a killer is lurking in your house, it's easy to find him. Medieval peasants had perfect teeth. Although in the 20th century it is possible to fire weapons at an object out of visual range, people of the 23rd century will have lost this technology.
All single women have a cat.
Any person waking from a nightmare will sit bolt upright and pant. Even when driving down a perfectly straight road, it is necessary to turn the steering wheel vigorously from left to right every few moments. One man shooting at 20 men has a better chance of killing them all than 20 men firing at one. Creepy music coming from a graveyard should always be closely investigated. During a very emotional confrontation, instead of facing the person you are speaking to, it is customary to stand behind them and talk to their back.