Today’s invention is a goblet (with opaque sides) and which contains a false bottom. This can be used as a joke for party guests.
Initially, the false bottom disguises a reservoir of liquid below it (A).
After some of the drink has been consumed (B), the lower plunger moves gradually upwards so as to make the level of the drink seem nearly the same as before.
This allows eg a party host (or bar owner) to encourage people to drink at a faster rate than the one they perceive (at least for a while).