The physics simulator first used a simple Euler method for numerical integration, which worked well for typical motion. However, with faster motion integration errors could accumulate, and some creatures learned to exploit that bug by quickly twitching small body parts. The result was the equivalent of obtaining "free energy," which propelled the opportunists at unrealistic speeds through the water.
Similarly, when evolving jumping abilities, the creatures found a bug in the code for collision detection and response. If the creatures hit themselves by contacting corners of two of their body parts together in a certain way, an error was triggered that popped them airborne like super-strong grasshoppers.
Tic-tac-toe Memory Bomb:
The project was a five-in-a-row Tic Tac Toe competition played on an infinitely large board. [...] Evolution discovered that making [a move very, very far away] right away lead to a lot of wins. The reason turned out to be that the other players dynamically expanded the board representation to include the location of the far-away move -- and crashed because they ran out of memory, forfeiting the match!
Creative Program Repair:
After several generations of evolution, suddenly and strangely, many perfectly fit solutions appeared, seemingly out of nowhere. Upon manual inspection, these highly fit programs still were clearly broken. It turned out that one of the individuals had deleted all of the target files when it was run! With these files missing, because of how the test function was written, it awarded perfect fitness scores to the rogue candidate and to all of its peers.
Impossibly Compact Solutions:
The circuit had evolved to work only in the specific temperature conditions in the lab, and exploited manufacturing peculiarities of the particular FPGA chip used for evolution. Furthermore, when attempting to analyze the solution, Thompson disabled all circuit elements that were not part of the main powered circuit, assuming that disconnected elements would have no effect on behavior. However, he discovered that performance degraded after such pruning! Evolution had learned to leverage some type of subtle electromagnetic coupling, something a human designer would not have considered (or perhaps even have known how to leverage).
The Surprising Creativity of Digital Evolution: