A scientist was trying to make a hair grower. But, it didn't work. he added secret ingredients and it worked on a frog, and it grew, so he removed it with hair remover, he threw the hair grower in the toilet, but forgot to flush. and it lived.
First, it can be seen in Captain Underpants Crunchy Book-o-fun #1,
Then, it appeared in Captain Underpants Crunchy Book-o-fun #2.