The peculiar slime mold is a single-celled creature with no brain (although in some stages of its life cycle, it looks a bit like a yellow, blobby brain), and yet it can navigate mazes and remember and anticipate environmental events.
...And no one is quite sure how.
Slime molds consist of colonies of many single-celled individuals that communicate with each other via pulsing; the type and speed of pulsation, likely determined by environmental variables sensed by the cells' surfaces, affects in which direction and how the whole organism moves. When scientists exposed the moisture-loving slime mold to dry conditions for 10 minues every hour, the mold learned the pattern and started constricting in self-defense in anticipation of the unfriendly conditions.
Perhaps more amazingly, slime mold can navigate mazes in the most efficient manner possible; by leaving a deposited trail of slime, the organism seems to use an external memory system that is an evolutionary alternative to our internal memory system (our brain!)
Before we spend more time searching for alien intelligence elsewhere in the universe, perhaps we should take at look at our own backyards: that yellow, blobby thing in the corner is quietly working to overturn all conventional notions of "intelligence."
"For a single-celled organism, it has continually surprised researchers with its abilities, such as solving mazes, anticipating periodic events, and even making irrational decisions like we do," he told BBC Nature. "It is truly a remarkable creature that is redefining our notions of 'intelligence'."