In case you missed it, Michael Phelps took home his 19th gold medal with three of his teammates in the men's 400M freestyle final on Sunday night.
The internet reacted to the exciting news and showed support for the most decorated Olympian, but that wasn't the only thing they were talking about.
As soon as he walked out to the pool, many were wondering why he had dark red and purple bruise-like marks on his back and shoulder?
It turns out the bruises are caused by a therapy called "cupping." Many athletes believe cupping helps them heal faster and relieves tension in their muscles. Suction cups are used to pull the skin up and away from the muscles. The suction only lasts a few minutes but it instantly creates a bruise, much like a hickey would.
Michael Phelps is even seen having the technique done to him in his Under Armour commercial. Check it out at the :45 second mark.
Less than a year ago, Phelps posted a photo on Instagram of Allison Schmitt helping him with his cupping. The photo got over 29,500 likes.
Therapy or not, twitter users had some fun with the cupping bruises...
Michael Phelps...is into cupping? Or fought an octopus? #Rio2016
— Ahab (@ahab99) August 8, 2016
Does phelps have those circle bruises from cupping massages or are they marks showing he's an alien fish in disguise... makes u think.
— Ahh, Diet Parpo|5| (@mtwundagore) August 8, 2016
The bruises even became a trending topic on twitter...