Humans often adjust their actions when previous solutions no longer work. Think of a woodworker carving spoons—depending on the type of wood, they must switch techniques to shape the spoon correctly. This ability, called behavioural flexibility, helps us solve new problems by adapting our actions. But do chimpanzees show the same flexibility, and if so, is it linked to their understanding of cause and effect?

To explore this, we present chimpanzees with a transparent tube filled with paper straws. Only one straw holds a grape, and its position changes throughout the test. To get the grapes efficiently, the chimpanzees must pull only the “correct” straws below the reward, suggesting they might understand the link between their action and the outcome (Figure 1).

In experiment 2, chimpanzees get a choice between two tubes. One tube is blocked with a paper ball under the grape (they cannot get the grape), while the other has a paper ball on top of the grape (they can get the grape). Therefore, if chimpanzees show causal understanding, they should prefer the tube where it is possible to receive a reward. To further explore this, we will also look at causal feedback by seeing how the chimps perform when they are presented with a transparent tube (feedback) vs an opaque tube (no feedback) and if they can apply reasoning when a tube is rotated in a final experiment.