The Sensed-Presence Effect

How the brain produces the sense of someone present when no one is there

In the 1922 poem The Waste Land, T. S. Eliot writes, cryptically: Who is the third who always walks beside you? / When I count, there are only you and I together / But when I look ahead up the white road / There is always another one walking beside you.

In his footnotes to this verse, Eliot explained that the lines "were stimulated by the account of one of the Antarctic expeditions [Ernest Shackleton's:] … that the party...