But you thought you were supposed to swallow it? Nope.
I had never heard of people rubbing castor oil on their bodies, and certainly not to aid with digestion. But apparently, it has been used this way for a very long time. Here are some facts from Wikipedia:
Undecylenic acid, a castor oil derivative, is also FDA-approved for over-the-counter use on skin disorders or skin problems. Castor oil penetrates deep into the skin due to its molecular mass, which is low enough to penetrate into the stratum corneum. Castor isostearate succinate is a polymeric mixture of esters with isostearic acid and succinic acid used for skin conditioning, such as in shampoo, lipstick and lip balm.
So it looks like this guy might know what he’s talking about.