I've often mentioned the dowsing demo I saw at the Rollrights, where the bloke was blatantly moving his hands to get a result, whether he realised he was doing it or not. "Is there a burial here?" *Moves hands to make rods rotate clockwise* "Yes!" Erm. No. Unless you buried someone there. ;) I don't know if there's a burial there. I'd guess not, but the point is, he moved those rods. A few gasps from people who'd not noticed, and you there's your believers! Maybe it was sheer coincidence and he'd inadvertently found an underground watercourse. :D
For what it's worth.... guess I should mention some years back - August 03 - I took my mum (very much open to new experiences) and my Dad (the complete opposite, won't even watch a biopic on Darwin) over to Kent and The Chestnuts. The lady who has the chamber in her garden hands out dowsing rods for punters to have a go.. don't know if she still does.
Anyway, I REALLY wanted it to work for me. Nothing. I think my mum had a little response....maybe. But my Dad? The rods were moving all over the place, absolutely freaking him - and us - out. He really didn't know what to say. Of course he could have had some subconscious reaction to his denial of such stuff (a case of 'The lady doth protest too much, methinks'). Or he could have been the perfect medium because he really, really didn't want it to work. Dunno.