Keeping zoo animals healthy is one of the primary responsibilities of zookeepers, and one of the best ways to check the critters' health is to have them hop on a scale. This is exactly what the keepers at the ZSL London Zoo went about doing for the zoo's annual weigh-in.

As the video shows, some animals are a bit easier to get onto the scale than others. Penguins seem content sit on the scale for as long as it takes, and gorillas don't mind standing next to a board that measures their height. Even a scorpion sits for enough time for zoo officials to get an accurate weight.

Other species, however, needed some coaxing.

Lions reach for treats so they'll stand up to their full lengths and zookeepers can see how much they've grown, and squirrel monkeys were lured with bananas over to a scale. Basically, bribery works wonders for the lions and the penguins. Bribery seems like it is less successful for the squirrel monkeys, however. They are happy to grab a treat and then scamper away. We hope the zookeeper has quick eyes and hands to jot down the monkey's weight before it runs off!

Editor's note: This story has been updated since it was originally published in August 2016.

Zookeepers get clever to weigh animals
It's no easy task weighing 20,000 animals at ZSL London Zoo.