More than 16,000 animals are getting weighed and measured at London Zoo's annual weigh-in.
From great apes to lairy llamas, all creatures great and small will have their measurements recorded - although some are h arder to measure than others.
The annual check is undertaken to ensure each creature is getting enough nutrients for their development.
Keeper Luke Harding says this is vital for the wellbeing of each animal.
All the weigh-in data is shared with other zoos around the country, a nd can be a good way to identify unforeseen pregnancies within some of the more endangered species.
So stepping on the scales for these critters is more than just a check to see if they're piling on the pounds.