During a visit to a club in 1775, Samuel Johnson was observed to put several Seville oranges into his pocket after squeezing their juice into a drink he’d made for himself. The friends who saw this “seemed to think that he had a strange unwillingness to be discovered.” Visiting Johnson the next morning and seeing the orange peels scraped and cut into pieces on a table, James Boswell asked about them:

JOHNSON. ‘I have a great love for them.’

BOSWELL. ‘And pray, Sir, what do you do with them? You scrape them it seems, very neatly, and what next?’

JOHNSON. ‘Let them dry, Sir.’

BOSWELL. ‘And what next?’

JOHNSON. ‘Nay, Sir, you shall know their fate no further.’

BOSWELL. ‘Then the world must be left in the dark. It must be said (assuming a mock solemnity) he scraped them, and let them dry, but what he did with them next he never could be prevailed upon to tell.’

JOHNSON. ‘Nay, Sir, you should say it more emphatically:–he could not be prevailed upon, even by his dearest friends, to tell.’

I don’t think this has ever been fully explained, but Boswell notes that, in a letter to Mrs. Piozzi, Johnson had once recommended “‘dried orange-peel, finely powdered,’ as a medicine.”