Castor oil applied to the cervix to induce labour!!!!????

I was at my docs appt a few days ago and I overheard another pregnant woman saying to the person sitting beside her, how she was going to insert castor oil, so that way it can be directly applied onto the cervix to induce labour. Now, i've heard of ingesting it, and rubbing it on the belly, but never inserting it lly. That blew my mind. Is this true?? i know that taking castor oil orally will cause mostly discomfort and diarrhea if taken before your body and baby are ready. I'm REALLY curious to know. I'm personally going to wait until the baby is ready on it's own. Thanks :o)