Ed Yong in The Atlantic:
Sometimes, Audrey Dussutour enters her lab in Toulouse to find that one of the creatures within it has escaped. They tend to do so when they’re hungry. One will lift the lid of its container and just crawl out. These creatures aren’t octopuses, which are known for their escape artistry. They’re not rats, mice, flies, or any of the other standard laboratory animals. In fact, they’re not animals at all.
They are slime molds —yellow, oozing, amoeba-like organisms found on decaying logs and other moist areas. They have no brains. They have no neurons. Each consists of just a single, giant cell. And yet, they’re capable of surprisingly complicated and almost intelligent behaviors. The species that Dussutour studies, Physarum polycephalum, can make decisions, escape from traps, and break out of Petri dishes. “It’s a unicellular organism but it looks smart,” she says.
At its smallest, Physarum can exist as microscopic cells, which actively swim about. These cells are attracted to each other, and when they swarm together, they can merge. The result is a single giant cell called a plasmodium, which can extend for meters.