Porta

For the Forerunner artifact, see Portal. A Porta is a sphincter-like orifice embedded into the floors and walls of Flood hives that acts as the Flood analog to doorways. Portas were sighted in the Flood-infested High Charity in the Halo 3 multiplayer map Isolation and on the Flood den in Halo Wars.

Trivia

 * Portas are comprised of seven segments, and there are seven Portas on the level Cortana.
 * The name "porta" probably comes from the Greek word porta (πόρτα), which means "door".
 * On the Halo 3 multiplayer map Isolation there is one Porta. Sliding down a hole on the top part of the map will lead the player to slide down a tube. A Porta will open, leading into a Flood-infested cave.
 * It is possible that Portas are not directly controlled by the Gravemind, as they always open for the Master Chief even when it is clear that the Gravemind does not want him to progress further.
 * There is a running joke among gamers that the Portas are the Gravemind's intestinal openings, due to their sphincter-like appearance.