If it was a ferrous metal table I woyld suggest magnetic induction from your house wiring causing an electromotor effect.
If non-ferrous material - a subsonic sound of high amplitude inducing a sypathetic vibration in the table top.
In both cases - it causes the saucer to rise up off the top of the table at the peak of the sine - causing it to move "downhill".
These theories can be tested with a ball bearing. If it is placed on the table in the same spot as the saucer - it should roll in the same direction that the saucer moved.
Or it's aliens.
One or the other......
If non-ferrous material - a subsonic sound of high amplitude inducing a sypathetic vibration in the table top.
In both cases - it causes the saucer to rise up off the top of the table at the peak of the sine - causing it to move "downhill".
These theories can be tested with a ball bearing. If it is placed on the table in the same spot as the saucer - it should roll in the same direction that the saucer moved.
Or it's aliens.
One or the other......