Plasma globe
Plasma lamps are very interesting, but rather limited toys.
Description: Although there are many variations, plasma lamps are usually a glass orb (much like a large light bulb) with a smaller orb in their centre. Beams/snakes of "light" (ionized gas) move from the inner ball the the outer glass container. See Electric glow discharge.
Touching the exterior orb grounds out the current, causing a single beam to snake around from the inner ball to the point of contact. The current does move into the object it makes contact with, as glass is not a perfect insulator when extremley high voltages are involved. It would not be able to ground itself out if this was not the case.
Be careful when placing electronic devices (such as a computer mouse) on the plasma lamp: not only may the glass become hot, but the high voltage may put a substantial static charge into them, even through a plastic protective casing.
See Also Lava lamp