Oysters must be fresh. Buy them from a fishmonger you trust. If an oyster is partly open or if the shell is damaged, then discard the oyster.
Don’t eat an oyster that is not fresh, like Mr. Bean did.
If you want to enjoy an apple, you take a bite and shew. Same with oysters. Don’t simply swallow it. The flavors and aromas develop in your mouth when shewing and help you fully appreciate the oysters (or apple for that matter).