Before you begin:
Place an oyster flat-side up on a work surface. Grip the oyster with a kitchen towel to help protect your hand (or wear a glove), leaving the narrow hinged end exposed.
Place the tip of the knife between the top and bottom shells just adjacent to the hinge. Press inward, twisting and wiggling your knife tip, to release the top shell. At first, it may seem like you aren’t making progress, but continue with gentle pressure.
Continue wiggling the knife while pressing inward until the shell pops open. Try to keep the oyster level so the flavorful “liquor” (briny, salty seawater) stays inside the deep bottom shell.
Wipe your knife to remove any debris, then pry open the shell by inserting the knife tip in one or two other spots, twisting it to release the shell completely. Continuing to hold the oyster level, run your knife along the inside of the upper shell to cut the muscle that attaches the oyster to the top shell.
Run your knife along the inside of the lower shell and gently cut the oyster free. Leave the oyster nestled in the shell. (If you open an oyster that has a strong, sulfurous smell, discard it. It’s dead.)