This story takes place on a Native American reservation. One night, it was very, very cold; so cold that people had to bundle together to stay warm.
Coincidently, nine months later, at the reservation hospital, there were so many women in labor on the same day that every bed in the maternity ward was full. When another woman came in, the staff found a deer skin and stretched it out on top of some pillows to provide for her a comfortable place to deliver. She gave birth to a healthy baby boy.
Another woman came in, so the staff found a buffalo skin and stretched it out on top of some pillows to give her a comfortable place to deliver. She gave birth to healthy twin baby boys.
Finally, yet another woman came in. The staff scrambled around, and found the skin of a hippopotamus (a traveling circus had been passing through the area earlier that year and their hippo had died...). They stretched it out on top of some pillows to give her a comfortable place to deliver. She gave birth to triplets - three healthy baby boys.
The story is just another validation of a well-known truism:
"The sons of the squaw of the hippopotamus are equal to the sons of the squaws of the other two hides."