In a general context leftovers after eating food are considered "unclean". Many people may not even wash their own plates at home - there would be a housemaid who does the job.
But switch the context to the temple people because of their tradition, belief system are ready to roll over the leftovers on leaf plates eaten by some else!
So the same mind which considers one thing as unclean can see the same as a very religious and hence "pure" thing to do in another context.
On the topic of the power of the mind, my wife (who is a doctor) says that in psychiatry they are taught about women who are infertile but the desire of having a child is so strong that they get all the symptoms associated with pregnancy except that there is no child growing the womb.
It is said the mind can be your greatest friend or your greatest enemy.
No wonder most of our spiritual teaching focuses on the mind!
P.S. Happened to come across this interview with Deepak Chopra on NDTV after writing this piece which also touches upon the power of the mind.