"Believe me, you don't want to get into the water with a hippo."

Their sweatshirts say they're from Vauxhall Primary. They're maybe ten, skin tones from chestnut to honey, hair in skinny plaits, in cornrows, scraped back, fanned out. And they are vibrating; at the age when they're high on hormones and glycogen, all angles and excitement. Four in a row, rocking left to right like the chromed spheres of a desktop toy; a secret passed from the first to the second, then the second to the third, then on to the fourth, then a gale of laughter.
'She what? Noooo! You lie!'
'I tell ya! She started devlelopin'...'
'Dev-what?'
'Devlelopin...'
'DEVELOPING!'
'Yeah! When she was seven!'
'O my days!'
More laughter, and another secret runs from mouth to ear to mouth. They rock with laughter, hands over mouths and then waving away the fresh scandal into the carriage.

Opposite them and next to me, screened from them by the standing commuters, is one of their classmates, nose sunk in a book. The pages turn. Her teacher reaches down, plucks the book from her hands - dislodging a playing card bookmark - looks at the cover and passes it back down. The playing card falls against my foot and I retrieve it for her; she glances up sidelong and mumbles thanks, inaudible.

The four girls opposite look her way. Just once.