In his letter of 22 December 1871 (Correspondence vol. 19), Galton had described George Butler’s habit of putting his arm across the top of his head when sleeping in a chair. His arm would eventually drop, hitting his nose and waking him. Galton had noted that Butler’s son, Henry Montagu Butler, and granddaughter, Agnes Isabel Butler, inherited this habit. See also Correspondence vol. 20, letter from Francis Galton, [before 28 March 1872], and Expression, pp. 33–4, n. 8. In a note in DAR 105: A77, CD recorded a correction from Francis Galton to the passage in Expression, replacing ‘striking’ with ‘stroking’ in the account of the granddaughter. The correction was made in Expression 2d ed., and the story here about the thumbnail was also inserted in square brackets by Francis Darwin (Expression 2d ed., p. 34, n. 8).