Do not open oysters until just before using. Scrub the shells to clean off any debris that clings to them. To open, hold the oyster in one hand protected with a clean, folded kitchen towel or set the oyster on a solid surface and hold it down against the surface with a clean kitchen towel. Either way, be very careful since the knife can easily slip.
Holding an oyster knife in the opposite hand, insert the blade into the crack between the shells near the hinge. Twist the knife to break the hinge, then slide the knife under the flat top shell. Cut through the adductor muscle near the top shell, taking care not to damage the oyster flesh or lose the juices. Remove and discard the top shell. Carefully cut the lower end of the muscle from the bottom shell to loosen the oyster. Carefully brush away any loose particles that might be left in the remaining shell. For traditional service, oysters are served in the bottom shell on a bed of crushed ice with a shallot vinaigrette (sauce mignonette) and garnished with thin slices of rye bread and lemon wedges.