Before revision: Etymology The meaning of the expression is attested from the early 19th century, and appeared in the Charles Dickens novel Oliver Twist (1838): Crows do conspicuously fly alone across open country, and crows fly in perfectly straight lines.
After revision: Etymology The meaning of the expression is attested from the early 19th century, and appeared in the Charles Dickens novel Oliver Twist (1838): While crows do conspicuously fly alone across open country, they do not fly in especially straight lines.