Following Ridley and the last surviving Metroid down to the surface of Zebes, bounty-hunter Samus Aran finds, amid the scattered remains of Chozo civilisation, a planet teeming with life. The statues left behind by the Chozo provide upgrades to Samus’ suit, altering its capabilities and allowing her to continue her explorations into once inaccessible areas. In addition to these character-altering modifications, other rooms through Zebes offer Samus the opportunity to resupply her Energy and Missile reserves, while returning to her ship will enable a complete resupply of Energy and inventory.
Alongside these explicit means of resupply the fauna of Zebes, when killed, may leave behind a pick-up that can restock a limited quantity of one of her expendable resources. What, if anything, the creature will provide upon death is dependent upon Samus’ current status; if any of her resources is at maximum a pick-up of that type will not be dropped.
Most creature types respawn when Samus re-enters an area, allowing them to be farmed to keep her Energy tanks topped up. One exception to this are the pipe based creatures that spawn every few seconds and travel horizontal across the screen. Because these creatures continually respawn without any action on the part of the player they provide a means of returning to full Energy and inventory without the need to exit and return to an area; they can be easily farmed for Energy capsules and other resources.
The various forms of pipe creatures make use of at least three separate but related mechanics and it is the relationships between these which allow them to function in the way they do. They are a classic example of dynamics at work, a change to any of the underlying mechanics would alter the way you interact with these pipe creatures. If they spawned in the same manner as other creatures, their use as a form of resupply would be no more effective than any of the other fauna found throughout Zebes. If the pick-up left behind upon death wasn’t related to Samus’ current status there would no longer be the certainty that every time they were killed they would provide something immediately useful, the act of farming them would become a gamble. Additionally, if firing beam weapons drained Energy, or if the creatures could only be killed by Missiles or Super Bombs, the benefits of killing them would be counterbalanced by the cost of doing so.
The function of the pipe based creatures is particularly interesting in that they allow the expenditure of time for resources. The ending of Super Metroid depends on the time taken to complete the game so utilising the resupply dynamic of the pipe creatures can get you out of a difficult situation at the cost of time which will affect the ending witnessed.
These pipe creatures are organic resupply points, where time can be sacrificed for a complete replenishment of resources. This dynamic is never explained, the act of discovery is a sign that you have developed an understanding of the underlying systems. You are rewarding for showing this understanding of how the game systems functions in a way that is entirely in context and non-patronising.