When a donkey tries to climb a steep staircase straight on, gravity pulls directly against its upward motion. The steeper the slope, the more force is needed to move forward — which makes each step harder.

But by turning sideways and cross-climbing, the animal changes the angle at which it moves against gravity. This reduces the effective steepness, spreads its weight across a wider base, and helps it stay balanced with much less effort.

The physics behind it is the same reason hikers and mountaineers zigzag up steep hills, a technique called switchbacking. Instead of fighting gravity head-on, you take a longer path at a gentler angle, which lowers the required force and conserves energy.

A simple movement — but a perfect example of how animals (and humans) naturally apply physics to make difficult climbs easier.