In the right-hand panel, in hell, a choir is singing from a score written across a man's backside. The notes are legible. In 2014 an undergraduate at Oklahoma Christian University transcribed them into modern notation, played them and put the recording online.
The music in the hell panel
Amelia Hamrick assumed the second line of the staff was middle C, as was usual for chants of the period, and wrote the thing out. She called the recording the five-hundred-year-old butt song from hell. It went round the world in days, other people played it on lute, harp and hurdy-gurdy, and CNN interviewed her about it.
Whether Bosch meant it to be playable, nobody knows; he may have been painting the look of music rather than a tune. What is not in doubt is that this corner of hell is built out of instruments used as machinery. A man is strung across the strings of a harp. Another is pinned under the neck of a lute. A third is inside a hurdy-gurdy. Art historians call the section the musicians' hell.
Now shut it
The painting is a triptych on oak panels, 205.5 by 384.9 centimetres open, with wings on hinges. Close the wings and every colour in it goes.
The outside is painted in grey-green grisaille: the world in the middle of being made, water, bare rock, the first plants, and not one person anywhere. God is a small figure at the top left with a book on his knee. Across the top, in Latin from Psalm 33, is the line ipse dixit, et facta sunt — he spoke, and they were made. So whoever owned it had to shut it to see the beginning. Grey, empty, silent, and then you open the wings and get paradise, the garden and hell in full colour. Most reproductions never show the outside at all.
Nobody knows what it is called
The title is not Bosch's. A 1605 description of the Spanish royal collection calls it the strawberry painting, after the enormous strawberries being carried about in the middle panel, and it was also catalogued simply as Lust. Five centuries of looking at it, and the best name anybody has managed is the one about the fruit.
The first record of it anywhere is 1517, a year after Bosch died, when an Italian visitor named Antonio de Beatis saw it hanging in the Brussels palace of Henry III of Nassau. No document says who ordered it, what it was for, or what it means.
From there it went to William of Orange, was seized by the Duke of Alba's men in 1568, and ended up bought by Philip II of Spain at auction in 1591 and sent to the Escorial, which is how a Dutch triptych packed with naked people came to hang in the palace-monastery of the most Catholic king in Europe.
Shut the wings and the world goes grey and empty. Open it for the strawberries and the choir.
Some stories are better over a coffee. Fifteen minutes with someone — audio only, not open yet.