you'll know when you'll get a "hit", it works differently for everybody I think, but you'll know it when it happens
basically you feel that the worm(s)/and or flukes etc. are getting it- feels like the spot(s) where you knew there's something there which does not belong there, kind-off "freezes"/stops moving and then you feel frequency working on it and then usually with large parasites you get a big BM or more of them soon after the "hit", because whatever is distroyed must go out and usually it happens very fast after the killing because the body tries to get rid of it as quickly as possible