A King's Guard horse decided to bite a tourist after she got a little too close to the animal while posing for a photo.
Footage of the incident has been doing the rounds online and has racked up hundreds of thousands of views.
In the clip, the woman can be seen standing next to the horse while someone attempts to take her photograph.
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But it seems the horse wasn't too impressed with the close proximity and swung its head around before clamping down on her jacket.
The woman stumbles back, obviously completely shocked by the sudden move, and steadies herself on the stone wall behind her.
The horse had actually been stood next to a sign that said: "Beware! Horses may kick or bite."
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It's best to steer clear of the King's Guard horses and give them as much space as possible.
A few years ago, a woman named Kirsty Curtis was by one of the horses on Horse Guards Parade when she decided to pose for a photo taken by her husband.
Instead of the memorable moment she had imagined, the horse snapped a bite at her arm at the crucial moment.
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While the bite did hurt and cause a bit of bruising, she didn’t ultimately end up having to go to hospital for it.
It left her with a warning to others, though.
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She explained: “We had taken my father Peter to London to see where he lived, as he used to live in Walthamstow.
“We went to Parliament to see PMQ’s with David Cameron and decided to have a walk through Whitehall afterwards.
“My husband decided to take a picture of me in front of the horse, but suddenly it bit me. It was shocking and did cause pain, but it is our fault.
“The soldier looked down at me and I could see by his face he thought ‘another one!’
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“I am an animal lover and we have to consider that these horses are just doing their job. If you get too close, you can pay the price."
The King's Guards have a hugely important job and are known for being rather stern.
In the past, they've been seen shouting at tourists who approach their horses or get in their way during a march.
Of course, horses can be skittish and unpredictable at the best of times, so walking up to one and trying to pet it is probably not a good idea.