Charles Darwin, blindfolded, smeared with tar and paint, shaved with a rusty iron hoop and tipped backwards into a tub of water: that was his 1832 equator crossing aboard the HMS Beagle. This episode explores the line-crossing ceremony, the centuries-old maritime initiation that divides a ship into uninitiated pollywogs and veteran shellbacks the moment it crosses the equator, and asks why isolated crews create such elaborate, chaotic rituals.

We look at a French ambassador buying his way out with silver in 1685, Joseph Banks recording the interrogation of ship's cats and dogs on Cook's Endeavour in 1768, and the modern two-day theatre of Wog Day and the Court of Neptune, complete with Davy Jones, Amphitrite, truth serum made of hot sauce and aftershave, and the greased belly of the royal baby. We also confront the dark side: sailors dragge ...