A nice animation highlighting the fact that without visual reference we cannot go in a straight line. It’s funny to see the routes people took in the experiments, even when driving.
Incidentally, even with visual reference, our walking in a straight line waves left and right. It’s not proof but here’s a picture I took of a Cornish beach which shows this:
I remember reading in (the late) Lyall Watson’s Gifts of Unknown Things how on the Indonesian island he visits, this means the footpaths have a natural rhythm to them as they sway through the landscape. Maybe like an English country lane, and not at all like a Roman road.