Rhinoceros by Eugène Ionesco (1959)

A rhinoceros comes thundering through the square of a drowsy French town one Sunday afternoon, and the locals, aperitifs in hand, fall to arguing not about the horror of it but about whether the beast had one horn or two. Then another, and a third. One by one the townspeople turn: skin greening to leather, a horn budding from the brow, the voice thickening into a trumpet, and each new beast insists, reasonably, that this is the most natural thing in the world. Ionesco watched friends in 1930s Romania embrace the Iron Guard, and he never forgot how politely, how sensibly, decent people talk themselves into the herd. The terror of the play is that it is also hilarious, the comedy and the horror the same green skin. At the end stands Bérenger, the shabby, hungover man who never fit anywhere, the last human left, refusing. You will recognise everyone who left him.