The Knight's Move

Talking to Ian McEwan - you'll see why in the next Sunday Times - we came upon the term "knight's move" when used about a certain type of thinking. I attributed it to Nabokov. But, as it happened, Ian was with some brain scientist who said it was a term originally used in diagnoses of schizophrenia. This is true - "Odd, tangential disruptions in the smooth continuity of speech." But, I discover, there is also knight's move drinking. This from the Rochdale NHS Healthcare Trust:
"Sir: We believe that we have come across a new symptom of schizophrenia and would welcome comments. A 38-year-old male, with a history of schizophrenia, was admitted following a disturbance at a public house. Our only source of history was the landlady, who described increasingly bizarre behaviour over the preceding 4 weeks. After purchasing a pint of beer he would take two steps forwards, take a drink, move a step to the side, take another drink, then return to his start by completing the rectangle.
We have searched the literature, finding no evidence of such actions and therefore suggest this is the first description of "knight's move drinking"."
Amazing thing, the brain, as, indeed, is chess.