Spinach
Spinach is a type of food that appears in select tins. Eating it will provide nutrition equal to a food ration (much more than other tins) and will increase your strength: "This makes you feel like Popeye!" (or "Swee'pea", if hallucinating)
Cursed tins of spinach contain a "decaying green substance"[1] which makes you lose strength[2].
The use of Spinach and it's effects in NetHack is a reference to comic strip character Popeye[1], who gains incredible strength after ingesting the vegetable.
