They noticed that some of Jesus' disciples failed to follow the usual Jewish ritual of hand washing before eating.
(The Jews, especially the Pharisees, do not eat until they have poured water over their cupped hands, a as required by their ancient traditions.
Similarly, they eat nothing bought from the market unless they have immersed their hands in water. This is but one of many traditions they have clung to -- such as their ceremony of washing cups, pitchers, and kettles.b)
Scripture quotations marked NLT are taken from the Holy Bible, New Living Translation, copyright 1996. Used by permission of Tyndale House Publishers, Inc., Wheaton, Illinois 60189. All rights reserved. (New Living Translation - The Bible Online)