Location

• Consider having a Halloween party, or at least part of it, in a cellar, a remote industrial estate or any other building that has a desolate or uninhabited atmosphere, and people will already arrive with unease, ready to be frightened. Create a scary but believable back story with elements of violent death, unhappy lives or unrequited love for the chosen place, and remember to include features of your chosen location in the tale. On the evening, tell the story to your guests while showing them around the place and pointing out the features, and your guests should be in for a sufficiently scary evening.
  
  

Appearance

• Well designed, realistic flesh wounds can have a scary effect on adults on Halloween. Instead of buying the ready-made wounds widely available in the shops, be more convincing with the help of your own moulage makeup design. Moulage are mock injuries applied to participants in emergency response exercises and the finished result can seem frightfully real. Several online resources offer free tutorials in moulage techniques, but you can also invest in a makeup artist who will apply faux wounds.
  
  

Props

• When using props, count on the unexpected rather than the obvious when scaring adults. Hang fishing lines from the ceiling in some parts of the house, including the bathroom or the kitchen, or place fake stains of vomit, brain matter or other indeterminable substances in a corner. A jack-in-the-box contraption that releases its spring when a beverage or bathroom cupboard is opened will make at least one of your guests jump, as will a radio-controlled toy rat behind the sofa.
  
  

Noises

• Sound effects can be scarier than any carefully placed props. Blood curling screams might be an obvious choice, but subtle sounds, including scuttling and squeaking rats, flapping bats, faint moaning or heartbeat sounds coming from the direction of the floor might have an even scarier effect on adult guests when staged at an unexpected moment. To make your guests duck, play the sound of an approaching train or the noise of a plane landing. If you lack the sound equipment, pop a balloon at a quiet moment during dinner and all your guests will jump. Scary sounds are available from a variety of online resources for free.