Game principle. The experimental task consisted in opening successive safe boxes using 4 keys that had to be dropped into 4 slots in any order (24 possible combinations). Each safe box displayed a single target composed from 4 triangles (black square on the left safe box). Safe boxes opened when players produced the unique combination that respected a simple rule unknown to them. In the Low Difficulty condition, the rule required individuals to drop the keys such as the left triangle on the first key (1) matched the left triangle on the target (1), the top triangle on the second key (2) matched the top triangle on the target (2), the right triangle on the third key (3) matched the right triangle on the target (3) and the bottom triangle on the fourth key (4) matched the bottom triangle on the target (4). Thus, the matching pattern went clockwise. Examples 1 and 2 display successful combinations. Note that keys’ colour and orientation are not consistent between combinations, yet they are both successful ones. Keys could not be rotated by participants. In the High Difficulty condition, the matching pattern did not go clockwise but was arbitrarily chosen (see Methods).