Thousands of animals at ZSL London Zoo – from the African bullfrogs to the penguins – are being weighed and measured as part of the annual weigh-in event on Thursday. /VCG Photo

It was not easy to weigh and measure these stubborn animals as zookeepers had to deploy tricks and ruses to convince these animals to step on the scales. /VCG Photo

The check-ups allow zookeepers to assess animals' general health and help detect pregnancies. /VCG Photo