Slime molds are gelatinous amoebae that are classified as protists, a taxonomic group. Slime molds, while brainless, are smarter than they look. Physarum polycephalum can solve mazes, mimic the layout of man-made transportation networks, and choose the healthiest food from a menu.
P. polycephalum rummages through leaf litter and oozes along searching for bacteria, fungal spores and other microbes that it envelops and digests. Although it acts like a colony of cooperative individuals foraging together, it spends most of its life as a single cell containing millions of nuclei, small sacs of DNA, enzymes and proteins.
It takes on different appearances depending on where and how it is growing. In the forest, it might fatten into giant yellow blobs or remain a smear of mustard under a leaf. In the lab, confined to a petri dish, it spreads itself thin across the agar, branching like a coral.
In the 2000s, Japanese scientists chopped up a single P. polycephalum and scattered it throughout a plastic maze. The slime eventually grew and found each other, eventually filling up the entire labyrinth.
The scientists then placed blocks of agar packed with nutrients at the start and end of the maze. Several hours later the slime mold had retracted its branches from dead-end corridors, growing exclusively along the shortest path possible between the two pieces of food.