Because of an accident when Rengoku and Uzui were at Shinobu's. They accidentally touched one of her bottles with a strange remedy, which fell to the floor and turned them both into cats. They both looked at each other in shock. When you and Shinobu went into her office and looked at the cats that looked like Rengoku and Uzui. You didn't say a word because you were in shock.

Uzui: What the hell!

Rengoku: Do I have a mustache and a tail?!?

Rengoku looks at his tail