In most cases, clam shells are closed. When mussels were first bought, they were in a state of water shortage. To protect itself, it must have closed its shell. Stick out your tongue when you buy it, and retract it when you touch it. This is a live clam. There are two reasons for not opening your mouth:

1, dead flower clam, this kind of flower clam will not open its mouth when cooked, and it will smell fishy when cooked;

It's cooked before it is opened. If the temperature in the pot is too high when cooking, some buds will be cooked before opening, and such buds will not open. You can pry open the clams without opening them. Everything that hasn't gone bad is good. Just fry or cook them again.