I was told a story some years ago, about a young man who apprenticed in a Japanese restaurant, where his main job was preparing the rice. He was instructed in a very specific manner of washing (rinsing) the rice before it got put into the rice cooker. He was to put the appropriate measure of rice into a vessel, which would then be filled with cold water. Then, he was to stir it counter-clockwise, and ONLY counter-clockwise, three times. Rice, it was explained to him, grows in a clockwise direction, and it had to be stirred counter-clockwise so that it would realize the life that it could have had, if it hadn't been harvested. Then, as he was stirring the rice, he was instructed to say a prayer of thanks to rice, for its sacrifice, and for providing nourishment and sustenance.

So perhaps pre-Christian Celts also held some sort of comparable, animistic or shamanistic beliefs that would parallel something like this. Traditional Japanese Shintoism believes that spirits (kami) inhabit everything -- from rice, to trees, to mountains, to streams. So a fairly elaborate system of doing things has been established in response to those beliefs.