Scheana looked as if she was going smile-free for the photo, but the horse quickly interrupted by lunging to the side and nipping at her arm, which was exposed by her sleeves black mini dress.
The reality star stumbled forward and had a shocked expression on her face that was obvious despite her massive sunglasses.
She let out a little yelp as she moved away from the horse, but the nibble was modest enough that she started nervously laughing at her companions as she walked away briskly.
As usual, the King's Guard member atop the horse didn't acknowledge the close encounter.
The video was posted by the account @kingsguardlondonsites, which has captured numerous tourists being bitten or bopped by the King's Guard horses.
Scheana appears to have made it to the account's page weeks after her trip to London, and it's not clear that the original poster even knew she was a public figure.
Around the same time that Scheana was bitten, another tourist had a much more severe run-in with a King's Guard horse.
Video of the event showed a woman in a Pink Floyd T-shirt getting close to the horse for a photo, after it already appeared to be agitated and had been seen nipping at other people crowding it.
She let out a scream as the horse leaned over to bite her on her arm.
The woman ran back toward her party, and a man tried to dab at her arm with a cotton swab, but the woman fell to the ground and appeared to fall in and out of consciousness.
The injury was apparently so serious that the King's Guard made the seemingly unprecedented move to point his sword at a cameraman before asking him: 'Can you go and get the police officer?'
Just this year, several tourists have been captured in photos and video being bitten and allegedly pushed to the ground by King's Guard horses.
Scheana originally documented her time in London shortly after returning back to Los Angeles with a video posted to her YouTube channel on July 24.
She was in the UK for what she described as a 'girls trip,' which included seeing Snoop Dogg and Dr. Dre in concert and making an appearance on the Saving Grace podcast.
The Vanderpump Rules fixture dropped by several landmarks and popular tourist spots, including the Victoria Memorial near Buckingham Palace and Big Ben.
On her final day in London, she and her friend Jenny took a cruise down the Thames, and they sailed under the picturesque Tower Bridge.
The beginning of her trip didn't go as planned, as her friend ended up having a delayed flight that made her miss the entire first day.
So Scheana improvised with a visit to a swanky cocktail bar and an evening walk around the city in her workout clothes, which she joked make it obvious that she was a tourist.
Following her return home, she took a high-profile spot as a judge of the Miss USA pageant in Los Angeles earlier this month.
She stunned in a sheer black mini dress covered in intersecting stripes.