Objects used in Experiments 1–3.

<p>Experiment 1 (A) used a red dumbbell and blue Kong-toy, while Experiments 2 and 3 (B) used a blue ring and purple ball pair and an orange bone-shape and pink ring pair. Note that the pairs used in Experiments 2 and 3 could be linked together (C) such that they could be placed onto the detector as a unit.