Can a plant learn to close its leaves on cue, the way a dog learns to drool at the sound of a bell? For six days, pair two signals together on 20 Mimosa pudica plants: dim the lights while also dropping the room temperature from 25 to 16 degrees Celsius. The leaves close each time. On the seventh day, drop the temperature again but leave the lights on. If the plants have been conditioned (trained to link the two signals), the leaves should still close. Watch all 20 plants on that final test day to find out whether Pavlovian conditioning (learning by association) works in the plant kingdom.