When a haunting is active, witnesses may report observing something moving - it could be one or multiple items. But if there is one item that seems central to the odd activity, then that is a 'trigger object' of that particular case.

It is also a common practice to use items during ghost investigation to see if a 'trigger object' can be found - something that will cause an active ghost to respond to paranormal investigators, proving the presence of an intelligent, invisible entity.