We collected objects that do not have any known biological significance for rats, which might not always be obvious. For example, we observed once that rats try to bury a ceramic incense burner, and realized that from their visual perspective the object might have resembled a face with a widely opened mouth.

Using a method developed by David Mumby, we glue our objects to the base of mason jars, usually with silicone or glue delivered by a heat gun. Attaching the object to the base of the jar allows fixing the objects securely to the base of the open field – the lids of the mason jars are anchored with screws to the floor of the open field so that a mason jar with the attached object can be turned into the lid.

Each object has a centre point around which it is maximally symmetrical. When the object is placed into an open field, its center points to the midpoint of the floor of the open field. We do this to provide similar visual scenes when rats approach the objects in the open field from different vantage points.