Mike's concern over the quartet's hygiene prompts a first visit to the launderette in almost three years, a decision made all the more urgent, and obvious, by the escape--and subsequent murder--of one of Vyvyan's deadliest socks.
Vyvyan's self-decapitation, having stuck his head out of the window (contrary to written warnings) as the train went into a tunnel, results in a muddy hitchhike.