Very cool...how the hell does it fill from the bottom, with no spillage??? Did David Copperfield invent this?
Magnets. The bottom of the cup is made from two magnets. A ring that is attached to the plastic of the cup and the magnetic surface faces the vessel, and a "floor" that floats up when filling pressure is applied, then snaps back down to seal. The "floor" can be kept for use as a refrigerator magnet.