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.

Inspired by a method introduced 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.