What is a common feature of the box trap that prevents animals from escaping?

A common feature of a box trap that prevents animals from escaping is the triggered door. When an animal enters the trap, it activates a mechanism that causes the door to close behind them. This design ensures that once the animal is inside the trap, it cannot easily exit. The mechanism is typically sensitive enough to respond to the animal's weight or movement, ensuring a swift closure that secures the trapped animal.

In contrast, spiked walls would pose unnecessary harm to animals, which goes against ethical trapping practices, while a net cover could allow animals to escape or be only partially contained. An untriggered door would not serve any practical purpose in capturing an animal, as it would remain open, allowing the animal to leave freely. Thus, the triggered door is the key feature that effectively maintains the trap's intended purpose of holding the animal safely.