There is an old wive's tale (mostly among parents with constipated babies) that you can temporarily relieve constipation by inserting a small piece of soap into the sufferer's rectum to prompt a bowel movement.
Here is an excerpt of the instructions from an article on healthfully:
Cut the soap into a small piece that is the thickness of the patients' pinkie. [...] slowly insert the soap into the rectum. Keep the soap in there for several minutes so that the body temperature melts the soap [...] As the soap melts, you will start to feel pain in the abdomen area and you will want to go to the bathroom right away.
Disclaimer: I do not intend to use this method; this is just something that I've heard over the years.
I've found sources on more trusted websites that indicate soap might be helpful, but they do not explicitly refer to this "treatment" method.
Science Based Medicine's Constipation Myths and Facts says:
Stool softeners are essentially soap, and the theory is that they make the stool easier to pass. Despite their widespread use, there’s no good evidence that docusate sodium or docusate calcium are effective for the treatment of constipation.
And the University of Virginia's Treatment of Chronic Constipation vaguely mentions "soap suds":
Soap suds: contain water with a small amount of soap. The soap is mildly irritating and stimulates the lower intestine to secrete water and salt.
Is the insertion of soap into the rectum an effective means of relieving constipation?