BBC: Experiments run by Christopher Reid and his colleagues at the University of Sydney, Australia, have revealed that, as slime molds move around, the single-celled organisms leave trails to mark where they’ve been. Neither a mold nor a fungus, slime molds are actually a eukaryotic microorganism called a protist. They use localized pulsations to expand and explore, and they leave a trail of slime in their wake. For the current study, Reid’s team members placed slime molds on agar plates and separated them from a food source with a U-shaped barrier. The researchers noted that the molds did not retrace the paths they’d previously taken. In the initial experiments 96% of the slime molds made their way to the food with an average time of 57 hours. When the researchers covered the agar plate with slime, only 33% of the molds reached the food within the 120-hour time limit.