You can record several scary sounds and play it back during your halloween party:
Uncooked rice poured onto a cookie sheet sounds like rain.Crinkle a handful of cellophane for a roaring fire.To get a good scream you can, well, scream.Snap carrots in half for the sound of breaking bones.Flap a plastic bag in front of the microphone for the sound of bats.Slowly blow bubbles with a straw into a bowl for that bog sound.
Crunching Bones Party Idea