Mar-Vell owned a Flerken named Goose, whom she had taken with her on Earth during her undercover mission. After her owner died, Goose lived inside the Joint Dark Energy Mission Facility for several years, until she was reunited with Carol Danvers, one of the few people she likes. Goose traveled with Danvers to the Rambeau Residence where she later meets Talos, whom is another of the few people she likes, and then to Mar-Vell's Laboratory, where she swallowed the Tesseract and fought some Kree soldiers using her tentacles. In the aftermath of the Battle at Mar-Vell's Laboratory, Goose was taken in by Nick Fury at S.H.I.E.L.D., where she later regurgitates the Tesseract.
Flerken have a unique physiology as they have pocket dimensions inside their bodies. This allows them to swallow objects for protection and regurgitate them later on, even being capable of storing things as powerful as the Tesseract. In these pocket dimensions, Flerken store large tentacles that they can deploy at will from their mouths to attack enemies and help swallow large objects.
- In the comics, the Flerken are a race of aliens that resemble Earth's cats, lay eggs, and possess multiple tentacles that can extend from their mouths, which hold pocket dimensions inside of them.