I loved this little interlude from Brian Harry's blog: Is your stomach bigger than your eyes?
As it turns out calves have a simple algorithm for navigation – If my head fits through it, I can go. The problem is that their shoulders are wider than their head and their hips are even wider yet. In fact, this behavior is one we take advantage of. We catch cows in a “head gate” when we need to work with them. The cow walks down a chute, sees a gap in the head gate and tries to go through it. The edges of the gate catch their shoulders and close, locking the cow in.