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. Camels and owls seem content sit on the scale for as long as it takes, and while the spider is a little fidgety, it seems like there's enough time 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 penguins march onto a scale as a new part of their morning feeding routine. Basically, bribery works wonders for the lions and the penguins. Bribery seems like it is less successful for the monkeys, however. They are happy to grab a treat from the scale and then scamper away. We hope the zookeeper responsible for the monkeys has quick eyes and hands to jot down the monkey's weight before it runs off!