How do bird nests stay together? Researchers unravel entanglement between stiff, straight rods

The concept of constructing a self-supporting structure made of rods—without the use of nails, ropes, or glue—dates back to Leonardo da Vinci. In the Codex Atlanticus, da Vinci illustrated a design for a self-supporting bridge across a river, which can be easily demonstrated using toothpicks, matches, or chopsticks. However, this design is fragile—pulling one of the rods or pushing the bridge from below can cause it to collapse.