I'm a bit of a noob with electronics, but this is my understanding of the mechanics at work here.
When you rub a balloon and pass it over your arm, you give the balloon a significantly different charge than the hairs on your arm. So, the hairs on your arm are attracted electrostatically to the balloon. The balloon will stick to your arm, or head, because it retains this charge. Neither your arm nor the balloon is a good conductor, so the charge doesn't transfer very quickly to you. This is why you can rub a balloon on your head, stick it on the ceiling, and have it drift down an hour or more later, as it slowly discharges until the electrostatic force can't hold up its weight. But in a very humid area, the effect won't last as long, as the humidity will help the balloon discharge faster.
Your Noch or homebrew handheld has grass, a sieve, and a wire connected to the surface of your layout. The sieve is energized opposite of the layout. The static grass in contact with the sieve acquires the same charge as the sieve. Opposites repel, so the grass bits shoot out of the sieve and onto the layout, propelled by both gravity and electrostatic repulsion.
Once the static grass touches the glue on the layout, it switches polarity, and gets a new charge from the grounding wire. (Some things acquire a charge more quickly than others; the grass apparently has much less trouble swapping charges than the balloon does.) Since every bit of grass is thus polarized, they're repelled from each other, and since the sieve above them is oppositely polarized, they're attracted to it. But, like a fly trapped by the surface tension of a glass of water, they can't escape the glue, or perhaps gravity (we're not dealing with a very substantial force here). The charge is too weak to pull them back up to the handheld, and if they were pulled up, they'd just get charged with the sieve and shoot back down to the surface again. (This effect is at work in what's known as
Franklin's Bells. For this application, imagine you put some rubber cement on one bell. The clapper would hit the cement, and stick, but still pull towards the other bell.) So, the bits of static grass stand up pretty straight in the glue. Then the glue dries, and they're stuck standing up.
Again, I could be wrong, this is just my understanding of the forces at work.
