> I also seem to recall a type of toy vehicle that was propelled by some compressed gas as it slid, suspended along a horizontal wire/string, but I'm drawing a

> I also seem to recall a type of toy vehicle that was propelled by some compressed gas as it slid, suspended along a horizontal wire/string, but I'm drawing a blank regarding the type of propellant right now. It seemed safe enough to use indoors, especially considering the constrained pathway. I've heard of using ordinary rubber party balloons for this.