Three days before the big video call between Joe Biden and Vladimir Putin, a train rushed through the village of Polushkino, 60 kilometers (37 miles) west of Moscow. It was loaded with military trucks, command staff vehicles and two dozen Tigr-M all-terrain vehicles.

A trainspotter with the username “dinisvogonov” filmed the train and posted the video to TikTok – one of the many, small pieces of the puzzle that observers are currently using to piece together a picture of Russia’s troop buildup near the border with Ukraine.