Based on something I first learned about on an episode of QI XL, this is in fact a very real thing. From wikipedia:
“For 1,000 days (a little less than three years) the priests would eat a special diet consisting only of nuts and seeds, while taking part in a regimen of rigorous physical activity that stripped them of their body fat. They then ate only bark and roots for another thousand days and began drinking a poisonous tea made from the sap of the Urushi tree, normally used to lacquer bowls.
This caused vomiting and a rapid loss of bodily fluids, and most importantly, it made the body too poisonous to be eaten by maggots. Finally, a self-mummifying monk would lock himself in a stone tomb barely larger than his body, where he would not move from the lotus position. His only connection to the outside world was an air tube and a bell. Each day he rang a bell to let those outside know that he was still alive…”
Comic-worthy material, I’m sure you’ll agree.
PS. There were 22 James Bond films, in case you’re wondering.
Even on day 56 of his ritual self-mummification, something kept gnawing at the Sokushinbutsu monk’s mind: did they end up making 22 or 23 James Bond films?