We don't really know where to begin on this one. Apparently, someone took a report from 2013, on a study that discovered not only the mouth is able to have taste receptors that are sensitive, but several parts of the body including the stomach, lungs, brain, and testicles are all sensitive to umami. Umami, the Business Insider defines it as "the amino acid taste of soy sauce."
So, there you have it. People are dipping their testicles into soy sauce to test out their taste receptors down there.
If by some reason you're compelled to look into these #soysaucechallenge... here you go.
Is it just us or are these viral challenges just getting more bizarre and icky?