Regarding W. D., Edsger

The cacti walked.

Their spines were long; their platyclades were thick, possessing a dark green hue. Great clouds of dust rose from behind them; their ranks were so vast as to resemble an army.

"Hm," Dr. Washvanpelt said, watching one of the cacti neatly avoid a rock. "Quite decent pathfinding. But what happens when I do this?"

He arranged a series of logs so as to block a large area, and then stood well back.

"Ha!" the good doctor laughed, watching the cacti bump into each-other and press themselves uselessly against the barrier as they slowly, inefficiently moved around it. "Pathetic! I could code a better algorithm in my sleep!"

"But could you write one that would efficiently handle ten-thousand cacti moving at a time?" came a question from behind. "When you're pathfinding for half-a-dozen units, the efficiencies are quite different - there is a necessity to economize on these scale!"

"Economy, yes, yes," Dr. Washvanpelt said dismissively, watching the cacti. "But this behavior - it's worse than poor. It's positively inexcusable! Surely you can have simpler algorithms operating for cacti moving without problems and more complicated ones for those which have encountered trouble, which you'd downgrade again only if too many began to encounter obstacles and overtaxed the..."

"Wait," he said.

"You're not my grad student."

"Indeed I am not," came the hissing reply; and there was something very cold against Dr. Washvanpelt's throat. "And I think you are in no place to criticize my algorithms: for your pathfinding was very poor indeed when it led you here, Doctor, to the place you will die."

"Why?" the doctor wailed, watching the cacti come nearer and nearer. "Why would you do this thing?"

"You should not have meddled in the affairs of Opuntia," cactus-Dijkstra hissed vengefully in Dr. Washvanpelt's ear;

and for the sake of the more tender of our readers, who might easily be offended or distraught at the graphic scenes which followed, our tale ends here.