Open your mouth.

When the oyster is alive, it will breathe and absorb nutrients through the opening. If the oyster is dead, the opening will be larger, the shell and meat will be separated, and there will be a smell. After death, oysters lose the ability to breathe and digest, causing the shell and flesh to separate and decay. It should be noted that the opening and closing of the oyster during the cooking process does not mean life or death. Closing means that the oyster's muscles tighten when it is heated, and opening means that the oyster needs to breathe and absorb nutrients while alive.