h a l f b a k e r y
The word "How?" springs to mind at this point.
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A handheld "pen" or lightweight pump that, at the push of a button,
ejects a steady stream or jet of colored gas from its tip. This gas has
the exact same density as air, so it hangs in midair without rising or
sinking. Potentially, in an environment without any air currents, one
or draw in midair.
[xaviergisz, Aug 04 2009]
||What stops the gas from moving after being ejected from the pen?
||would need to be a long pointer to work, not a pen... but neat [+]