Look at that cluster of people across the street from Whitehall, in Westminister. They're looking at horses!
More precisely, they're looking at two mounted Queen's Life Guard (wearing red tunics and white helmet plumes). They're stoic men, frozen in a pose of immense concentration. I've seen people try to distract them, but it's very tough to do. These guys are highly trained professionals, and they're focused on their job. The building they're standing in front of is also known as the Horse Guard.
There's a sign warning people not to get to close because the horses may bite or kick. I've not witnessed it, but you can find online videos of that happening if you're so inclined.
Besides the mounted guard, there are also several foot soldiers on duty at Horse Guard.
The changing of the horse guard ceremony occurs at 11:00 am or 10:00 am on Sundays in the spacious grounds at the back of the Horse Guard building. I've witnessed it on one occasion, during our honeymoon in England, when the rain was coming down in buckets. It lacks the pomp of the Buckingham Palace changing of the guard, but is still very interesting to see.