This is how I have story ideas.
I was driving along a semi-major non-highway: one of those two-lane roads which goes stores-farmer's markets-banks-housing development-offices-woods-repeat for ten miles. And as the farmer's market was fading into the rear view mirror, I checked the road ahead of me -- and wound up swerving hard, avoiding the tortoise who was starting to cross by a good margin.
My next reaction was panic, because that tortoise was still crossing the road, that was going to take a while, and it was sort of low to the ground: there was a chance someone wouldn't see it in time. Plus I was already past it, so trying to stop --
-- was being taken care of. Because the car behind me swerved onto the shoulder, and I had just enough time to see the driver starting to get out. The tortoise had picked up a safety escort. Crisis averted.
And then I pictured Tank walking across an open area.
It took some refinement, and I needed a while to decide on the location. But it wound up as about 8400 words, along with a tribute to Far Too Many Things Funny And British. And how did that part happen? Because I wanted it to be a comedy and once I had Trottingham as the location, the rest just lined up.
So tortoise crossing two-lane road = this.
Your lesson, as always: writers are weird.