What other options did the zoo staff have? In the past, the threat of a dart gun could scare an animal away, or keepers would enter the enclosure with CO2 fire extinguishers. However, these days most zoo animals are trained to comply with veterinary and husbandry procedures, so many won't even recognise a dart gun, while extinguishers are now considered too risky to the health of animals and anyone in the pen with them. So, advances zoos have made through husbandry training mean that some "old" tricks no longer work. "Carrots" have been so effective we've forgotten about the "sticks".