When I was young I love to eat santol especially with salt on top. The always precaution my mother will tell me is to never swallow the seed. Anyway, swallowing it is almost impossible for me, as most of us know, santol seeds are large and it is difficult to swallow especially if you are a small child.
When I ask why it should not be swallowed my mother would tell me that it would not be digested and will lodge in my intestine and grow.
Today as an adult (sometimes) I do believe it is just a myth. There is no way a seed could grow inside a human body. But until recently, I am having second thought especially hearing about the news that a man was operated and found out that a fir tree have grown on its lungs. Whether a freak of nature or what ever , I would stay away from swallowing santol seeds.