My favorite explanation of the difference in difficulty between flat, right-branching, and left-branching trees comes from Dr. Seuss’s Fox in Socks, who takes a flat clause with three branches, each containing a short right-branching clause, and recasts it as a single left-branching noun phrase: “When beetles fight these battles in a bottle with their paddles and the bottle’s on a poodle and the poodle’s eating noodles, they call this a muddle puddle tweetle poodle beetle noodle bottle paddle battle.”
