The theatre is about illusion, but its effects can be all too real. The Victorians loved turning the stage into a lake for sea-battles in which swimmers manipulated large model ships; when Phantom opened at Her Majesty's, the theatre simply reverted to its original function as a site for spectacle.
And Covent Garden has always gone that extra mile: one wonders how the real horses in their Carmen and Katya Kabanova are restrained, night after night, from shying at the lights and dropping a memento. And when L'elisir d'amore is revived on Tuesday, the props will include not only an obedient dog but also a giant haystack alternating with a full-size trattoria, and a seven-ton lorry.
The main problem, says production manager Chris Harding-Roberts, is the fact that these props were designed for the much larger stage at the Paris Bastille: the 40-by 20-foot haystack fills Covent Garden's stage to bursting, and the giant lorry on which Dr Dulcamara appears with all his tricks has necessitated complicated stress-tests by engineers.
What's the hardest challenge he's had? 'The flames of hell at the end of Don Giovanni. We had to use a natural seed powder called lycopodium. Drop a lighted match into a pile of it, and it won't burn. But disperse it into a fine mist near a candle flame, and it turns into a fireball.' Tricky. And by the way, he says, those horses aren't totally dependable: "We sometimes have to run round after them with a pooper-scooper."
'L'Elisir d'Amore', Royal Opera House, London (020-7304 4000) 12 May