Lionel A. Tollemache, Recollections of Pattison:
“This masterful mode of translating tallies well with his strong desire that his pupils and friends should always use the best phrases and forms of speech. He [Mark Pattison] protested even against the common error of calling a sarcastic smile a sardonic one. He and I once talked over the old tradition a tradition mentioned, I think, by a Scholiast on Homer from which the word ‘sardonic’ is said to have sprung. In very early times the natives of Sardinia were wont to eat such of their country- men as were worn out by age. But, as manners grew milder, it was not thought seemly that a patriarch should be thus doomed without his own consent; and, in proof that his consent was freely given, he was himself chosen to bid the guests. Such, however, was the force of public opinion (opponents of euthanasia should make a note of this) that the veteran always issued the invitations to the supper where, in Hamlet’s phraseology, he would not eat but be eaten. The courteous smile which beamed on the old gentleman’s countenance as he was doing this last act of hospitality ἑκὼν ἀέκοντί γε θυμῷ is the prototype of all sardonic smiles. For the truth of this ghastly story the Rector would not vouch; but he insisted that the word ‘sardonic’ should be used in the sense which the story indicates. In short, he wished his pupils to remember that a sardonic laugh is a laugh at one’s own expense, and on the wrong side of one’s mouth. From the following remarks, it will appear that he himself laughed sardonically at the world.”
There is an interesting proverbial tradition behind this too.