A haunted helium balloon for Halloween (or any other time of the year!) This can really scare you, if you aren't careful!
one Helium Balloon (on ribbon or string)
one wrapping paper "ghost" (this is the ballast)
Step 1: Unweight
When you get a balloon, it usually has a weight on the end of the ribbon, to keep it from floating away. (pic 1a) Some times these are plaster, or a bag filled with either sand or beans. For our purpose, this is too much weight, as we want the balloon to float in an eerie manner. To facilitate this, replace the weight with a "ghost" made of paper. (pics 1b & 1c) Roll up a small ball of paper to put inside another small sheet of paper, to make a ghost. Tie him onto the ribbon.
Step 2: Trim the Ballast
You Are Going To ballast the balloon to about chest height. Do this by adding or subtracting weight. Losing ballast is easily accomplished by snipping away at the ghost's tail. (pic 2a) To add ballast, you may have to make a bigger ghost, or possibly add tiny bits of duck tape. Maybe you'll need a smaller ghost. However you can accomplish it, the goal is, for one moment, to get the balloon to just hang there, at about chest level, and not rise or fall. Do this in the middle room of your house.
Step 3: Wewease Bwian!
Once you've gotten the balloon (w/ ballast) to confidently HOLD there for a few seconds, let it go. Right there. Then forget about it. Go about your business. Go do laundry, or cook something. Watch TV. Lah dee dah.
I'm telling you, these things have a mind of their own. They will go from room to room periodically. You will wonder where it's gone, then it will suddenly appear. I've had one follow me clear through the house, ducking under the doorway. Waiting. It watches you. It's alive.
If you find it stuck to the floor in the morning, remove tiny tiny amounts of ballast, always initially looking for that "about chest height", and forget about it. Make adjustments if you have to. Give it a good try! It works! (just watch out for fans and open windows!)