Cat balls may the simplest tool in the box but are very, very effective and in terms of impact on those watching never fail to illicit a thrill.
These can be purchased at any pet store, most large supermarket pet departments and on many online venues.
Simply set a cat ball on the floor or any other flat surface and ask for the entity to touch the cat ball in response.
I have to admit that as long as I've been investigating and with all the things I've seen and heard I still get an enormous kick out of seeing a cat ball response.