 For Cavendish, both of the causal participants of a sensory perception are active, which is to say that the sense organ – usually regarded as passive – is  active.[33]  The body that is perceived is also a cause; it is what Cavendish calls an occasional cause: “I say that some things may be Occasional causes of other things, but not the Prime or Principal causes…” (Cavendish 1664, 79). Commentators have worried that even if we allow Cavendish the view that bodies are active and vital and the source of their own motion, she has no way to account for how it is that bodies communicate so successfully with each other if nothing is transmitted between them. Bodies seem to “suggest” (Detlefsen 2007, 168), or “induc[e]” (O’Neill 2001, xxx), or perhaps they transmit “a sort of signal that triggers the self-motion” of the body that moves (Michaelian 2009, 47), but the question is how they do this. As Detlefsen writes,