Chaos theory.

"How do porcupines mate?"
"Old joke. Very carefully."
"Or... unsuccessfully. Don't see many porcupines around."
"Creatures with highly evolved defence systems-"
"Like porcupines."
"-Like 42-year old successful self-involved loners. If you've found a female mirror image and think you're gonna form a rewarding relationship..."
"Think again?"

- The Thomas Crown Affair (1998)