PETROL strimmer lying in the grass. Choke turned on. Fuel turned on. I pull the cord once, twice, and on the third pull the engine barks into life. I increase the revs. But instead of a continuous, single-cylinder whine I hear a dull chug-chug indicating something is coiled around the cutting head. A piece of wire, brambles, end of a washing line, something like that. I flick the switch to cut the power. A ball of grey, black and silver unravels from the cutting head as the engine stops. It’s a snake.

Horror. The snake is wriggling in a patch of sunlight beneath the trees. It’s not going anywhere – just wriggling. I don’t know what to do except stand transfixed as it writhes and buckles, its belly to the sun. How did this happen? How did a snake become entangled in my strimmer?

I slide a stick underneath the snake and ease it over. It’s an adder, about sixteen inches (40cm) long. There is no obvious injury; no deep welt where the tough nylon strands have snared its body and whirled it round. But it feels pain. Snake pain. And snake shock, I suppose.

What should I do? My first thought is to kill it. Find a spade. Slice. But it’s a panicky thought and is soon replaced by reasoned indecision. I just stand and watch until the writhing subsides and the snake adopts a more natural motion.

The snake’s black eye is observing me. It’s one of those eyes that gazes everywhere at once, missing nothing – shiny and deep and hurt. I need to know what it’s thinking, this snake. I feel guilty though I don’t believe I should be blamed. How do you reason with an injured snake? And how do you say sorry?

After an interval I wander off and strim some ground on the far side of the garden, but every ten minutes or so I am drawn back to the snake. On my third return the snake has vanished. I search the area carefully several times during the day, but there is no sign of the injured snake. I suspect it has disappeared into a wall, gone back to snake world.

Next morning I return to the patch of sunlit grass where the adder had been basking. No snake. I search the walls and places suitable for snakes to venture. I will search again tomorrow because I feel sad and guilty, and slightly ashamed that my first thought was to kill it with a spade.