Sometime later, Yoshi adopted four turtles after they were accidentally dropped into the sewers by an unnamed boy. He returned from his explorations around New York City one day to find the turtles covered with a strange glowing ooze. This substance caused the turtles, who were most recently exposed to Yoshi, to become humanoid, while Yoshi, who was most recently exposed to sewer rats, became a humanoid rat, and was given the name "Splinter" by the turtles. Yoshi raises the four turtles as his sons and trains them in the art of ninjitsu. He names them Donatello, Leonardo, Michelangelo, and Raphael, after his favorite Italian renaissance artists.