Vacuum activities (or vacuum behaviours) are innate fixed action patterns (FAPs) of animal behaviour that are performed in the absence of a sign stimulus (releaser[broken anchor]) that normally elicit them.[1] This type of abnormal behaviour shows that a key stimulus is not always needed to produce an activity.[2] Vacuum activities often take place when an animal is placed in captivity and is subjected to a lack of stimuli that would normally cause a FAP.[3]