Note: This one has some elements borrowed from Ace Ventura: Pet Detective. Kudos to Jim Carrey.
We find one of our heroes, Brock Harrison, at Professor Oak's Lab. Apparently Brock had a sudden urge to show the old goat (i.e. Prof. Oak) some pictures.
"You notice anything Professor?"
"Not really. All I see is Professor Ivy's rear."
"Are you blind Professor? You don't notice the bulge in her panties?"
"Well I'll be. I never knew Dr. Ivy had hemorrhoids."
"Those aren't hemorrhoids! That's Mr. Winky, her pet Ekans!" Professor Oak's eyed widened.
"Please excuse me for a moment." Professor Oak darted to the bathroom.
You could hear the sound of an old goat spewing chunks.
To Be Continued….
To sum it up: this is why Brock ran away from Professor Ivy.