On Wednesday, ZSL London Zoo held its annual weigh-in to assess the growth of its 17,000 furry, scaly, feathered and slimy animal residents.

The audit, for creatures of all sizes and species, is also useful for detecting pregnancies, monitoring eating habits, and creating records that are sent out to other zoos for comparison.

While some critters, like penguins, get weighed frequently and do so with relative ease, others are a bit trickier. Monkeys pose one of the greatest hurdles and require some clever corralling.

"We have to use quite ingenious tactics to measure some of the animals," London Zoo press officer Rebecca Blanchard told the International Business Times. "We have to trick some of the animals into being weighed. For example, [for] the Galapagos tortoises, we disguise the scales as a patch of grass underneath the main lawn in their paddock."

Getty Images

For more dangerous animals, scales are built into their exhibits to get stats without putting the zookeepers in danger. For very small animals like snails, specialty devices are used to register their miniscule heft.

Getty Images

To see some of the weigh-ins in action—including a 1500 pound camel—watch the video below.