As I tend to brag about on a regular basis, I can read Thai. Therefore, when i see something strange I usually will have the reaction of "there is no way that is a real thing!" but in this particular instance, yes; yes it is a real thing. It is pronounced "Kai EE-oh maa" which literally translates to horse pee (piss) eggs.
There are rumors about the eggs (normally chicken or duck eggs but other eggs can be used also) being preserved in urine thankfully is not true. The reason why they are called this is because of the preservation process, they have a strong smell of sulfur and ammonia and well, they look pretty awful. They can be made to be less black but if you want them in their true, nauseating glory, eat the black ones.
This is originally a Chinese creation, who refer to them as "century eggs" and I have no idea why the Thais don't continue to use that name. They kind of do their own thing over here. Also these eggs are not a hundred years old (they may have been at one time - i dunno) but the actual process takes a few months. The process can be sped up (apparently, i read this online) by adding lead oxide to the mix. As with most things, the word "lead" normally means dangerous and in this particular scenario it can be poisonous.
These eggs are a delicacy in China and while it is less popular in Thailand there is plenty of these eggs on offer. I find it a bit difficult to get past the smell and this is the same problem I have with Durian.
The preservation process involves exactly zero pee. Instead wood, salt, ash, tea, lime, and clay are used. I can't even imagine who came up with this idea. It just goes to show that people will do just about anything.
I tried one, and maybe I am doing it wrong but I won't likely try another one. I was delighted to find out that there isn't any sort of horse piss involved in the process, but for me this is just a very strange food item that I am happy I tried it, but am very unlikely to consume again.