Zoo keepers across the country have been counting up all the animals and insects in their care.
As you can imagine, it's a massive job, so Newsround's Sonali went to find out how it's done...
You probably think nothing of registration every morning at school... but did you know that it happens to zoo animals too?
Today, zookeepers across the UK were doing what's called their annual stock-take.
It's basically a head count of all the animals and insects that live at their zoo.
I'm lucky enough to live only a mile away from London Zoo, so I went to check out how they were doing theirs.
But why do they need to do one in the first place?
To check if someone has pinched a penguin or run away with a roaring lion?
Well, the main reason isn't as exciting as that. They have to do it to keep their zoo licence.
But it's also important to help update the national register of zoo animals, which is used for breeding.
Visiting a zoo is always fun, but how interesting can just watching someone count them be?
Well actually it was hilarious seeing zoo keepers have to count the same kind of animal over and over again so photographers and camera people could get enough pictures.
I decided it was more interesting to go off and count some myself.
I started off somewhere easy - the lion cage.
It's one of my favourite animals, so any excuse to see one!
They only have two at the zoo. Though one of the keepers did try to scare me by saying there should have been three!
I did believe him... but only for about five seconds... you should have seen the look on my face.
Next up, the penguins. But how do you count up animals that are difficult to tell apart?
The only way you can tell whether a penguin is a male or a female by doing a DNA test.
London Zoo has a boy penguin called Caroline and a girl one called Bob because they were named before DNA tests were easy!
That's why each bird has a tag on their wing with a number on it.
So penguin counting isn't too tough, but can you imagine trying to count insects?
I tried the butterflies, but I found it impossible to tell whether I'd already counted one or not.
The flying around really didn't help either.
By the end of my visit, I found out that London Zoo has two lions, 43 penguins, 24 flamingos, 10 otters, around 250 butterflies and five or six meerkats (keepers think one of them may have had a baby last night, but can't be sure).
So what's the total tally?
Well, when I left the zoo, they hadn't finished their sums yet, but they do know they have 650 different species and last year, they had 15,104.
That's a big count!