Three years ago, artist Simon Weckert noticed something unusual at a May Day demonstration in Berlin：Google Maps showed there was a massive traffic jam, even though there were zero cars on the road.
Weckert realized that it was the mass of people, or more specifically their smartphones, that had inadvertently tricked Google into seeing gridlock on an empty street.
Weckert borrowed phones from friends and from rental companies until he had acquired 99 devices, which he piled into a little red wagon. Over the course of a day, Weckert would walk up and down a given street, towing his smartphone-packed wagon behind him.
Weckert says his wagon would create a long red line in the app, indicating that traffic had slowed to a crawl—even though there wasn’t any traffic at all.
demonstration：名詞，示威遊行。例句：They organized the demonstration against the new policy.（他們舉辦示威遊行，抗議新的政策。）
traffic jam：片語，交通阻塞。例句：I will be late cause massive traffic jams.（我會遲到，因為路上塞得很嚴重。）
pile：動詞，堆疊。例句：I piled a lot of books on the table.（我在桌上堆了一些書。）