Poem of the week: Iota and Theta … by Osip Mandelstam

‘No tongue can force words through it.’ Photograph: Lanmas/Alamy

Iota and theta, the flute
of the Greeks gives no recitals –
unsculptured and short of repute,
trench-crosser, it ripened and tightened.

You can’t let it out of your grip:
clench your teeth, you won’t subdue it.
You can’t pull its form from your lips.
No tongue can force words through it.