A man pulled a knife out on the train back from Paris today. I'm still shaking and my cheeks are still flushed. We looked up from our conversation when we heard a man shouting about some other passenger for not giving him a cigarette. It escalated until it became clear that the shouting man was not well. He lost control like I've never seen anyone lose control. The striding, the flailing of limbs, the screaming. I thought, "how fascinating that he's mixing at least three languages together in his rage". There was "Je vais te couper le visage, putain" followed by "Suck my cock", and then words which were neither French nor English, but some African or West-Indian language or creole.

Then I came to, and thought, "His venomous spit is landing on my face, he's so close." I stared at my scarf, and whispered to Miriam to do the same. The man kept striding up and down the aisle. When his back was turned, I suggested we should read something, because staring fiexdely at a scarf is not subtle. All we had to look at was the brightly-coloured collection of postcards we'd bought at the National Picasso Museum. Picasso. He's the kind of artist that draws attention to a person.

Eventually he stopped moving his legs, when he was parallel to us - so close that my ears hurt with his shouts and I was speckled with his saliva. He had been pushed so far that he had begun to fumble around in his coat, looking for something. In a flash, I realised that if he found it and whipped it out, its arc would be interrupted by Miriam's face. The two young men in the carriage stood up and I took that as his, and therefore our, cue. I shouted "Go, and duck". Or maybe Miriam did, or maybe neither of us did.

We ducked and went. Pushed past him. I don't run, but I think I must have been hurtling, because the next thing I remember is seated people's faces flashing past me. For carriage after carriage, until we couldn't go any further and collapsed into seats and each other's arms. We could barely get a grip, we were trembling so much.

We finally arrived at Mantes, and saw a sight through the window that somehow calmed us. There were about eight gendarmes standing in a circle around the man. They were listening to him. They were giving looks that gave the impression they understood him, and would let him say his piece. They seemed to understand, as Miriam and I did despite our terror, that he needed help - not to be locked in a cell for a night.

I can't see the funny side of this yet, but when I do, I think it will have something to do with never refusing a cigarette to anybody.