Professor Dingle led his guest into his lab. "Here are the specimens.
No one has ever seen this species of fly before."
Harvey was skeptical. "How are your flies different?"
"I'll show you." Professor Dingle walked to the back of the room
toward his insect observatory. As they walked past a row of fish
tanks, Harvey was struck by the odd appearance of some of the fish.
"What are these?" he asked, pointing to the fish.
Dingle smiled. "Those are male stickle-backs. They're genetically
programmed to attack anything with a red dot on it.
Harvey was surprised. "I didn't know that was possible."
Dingle pointed to his observatory equipment. "Then you'll be even more
surprised when you learn about my flies. Sit down there and look at my
new pets."
Harvey peered through the magnifying glass at the flies. "Why, they
have a tiny hourglass design on their back!"
"A recent mutation. I call them time flies. But the hourglass isn't
the only unusual thing about them. Notice where they gather together."
Harvey studied the scene before him. "I don't see anything unusual."
Dingle smiled. "Focus on the background. They're genetically
programmed to be attracted to a particular geometric shape."
Harvey studied the background again, and burst out laughing. "Now I
get it! Time flies like an arrow!"