The London Zoo on Thursday embarked on one of its trickiest annual tasks - the weigh-in.
Bullfrogs, pythons and penguins were among creatures being coaxed, often with food, onto the scales for the check on their weight and size. This allows keepers to assess the animals' general health, find out about pregnancies, when they are about to moult, and helps in the administering of medicine according to their weight, said the Zoological Society of London.
However, actually getting the animals to cooperate is no easy task. Zookeepers have to use ingenious methods. Penguins are "tricked" into walking over scales as they line up to be fed, while lions are encouraged to reach their full height by stretching for their breakfasts, which are dangled from above.
Not all of the more than 19,000 animals across over 560 species will be weighed. Sometimes, just one in a colony or group will be measured.
The annual weigh-in will take about a week to complete.