"Well, this—the locals call “Swooping Evil”—not the friendliest of names. It’s quite an agile fellow."
-- Newt Scamander (WFT)
A small spiny cocoon houses the large flying creature known as a Swooping Evil, and contains a “luminous venom” which can be squeezed out and used to remove unpleasant memories (WFT). The cocoon unravels to release the creature, and closes up again when the Swooping Evil returns.
The way the large Swooping Evil could fold itself back into a cocoon small enough to fit into Newt Scamander's pocket means that like the Occamy, a Swooping Evil may be "choranaptyxic" or able to fit into the available space. This point is not canon, however, since Newt only mentioned that trait for the Occamy and not any other creatures.