Mussels in a pot
The Rule About Not Eating Closed Mussels Is Actually Complex
While common food lore dictates that a closed mussel is bad, science disputes this. In fact, some open mussels can also be problematic.
Experimentation shows that mussels close their shells due to stress like heat exposure during cooking. Their shells usually open when the muscle becomes weak while cooking.
Mussels that stay closed aren't dead, and they aren't likely to cause any problems when the shells are pried apart.
Food scientist Nick V. Ruello disrupted conventional notions about unopened mussels, revealing that certain mussels' shells could open even without proper cooking.
As a result, a closed mussel has the same chance of making you sick as an open one — making it imperative to smell your seafood to detect any bad odors before cooking them.