Could it be possible that the concept of ley lines arose from the observation of remnants of Roman roads? During the dark ages uneducated folk could have seen these straight tracks running across the country, many of them going nowhere obvious and attributed supernatural origins to them.

Dowsing, now there's an interseting one. As you say it could be possible for water to have a physical effect. However I have seen staged demonstrations fail miserably. The continued belief in the process could be due to the fact that there is a lot of water underground (ask any tunnelling engineer) so that random digging is often sufficient to hit water.

Stone sexing. Someone is pulling your pisser.

Bert.