This curious item consists of two small mirrors, each about the size of an average human palm. It is activated by speaking two command words, one of which is engraved on the back of each mirror. It may be deactivated by touching both mirrors at once and speaking the command words again.
When activated, a small two-way portal is opened between the two mirrors. Light, sound, air, water, and small objects may pass through from both sides. Differences in air or water pressure will cause gases or liquids to flow from the side of greater pressure to the side of lesser. Naturally, the rate of flow increases with pressure difference; water will gush through a portal on the bottom of a deep lake much faster than through one lying in a puddle.
The two mirrors must remain on the same plane of existence for the portal to function.