A fish biscuit, along with some animal feed and water, was the prize for operating the three controls of the "complicated gizmo" in Sawyer's cage on Hydra Island. Tom told Sawyer that the bears had solved the cage's puzzle within two hours, which was confirmation that polar bears may have been part of a DHARMA Initiative project. This had been previously hinted at but not confirmed from a brief scene in the Swan Orientation Video.
Sawyer gave his fish biscuit to Kate at the end of "A Tale of Two Cities"; later she asked him to get her another one but he believed the request was just an attempt to "keep [him] feelin' productive."("I Do")
- YTMND - Article includes a list of fish biscuit-related YTMND animations