I always like this one. Not mine, though.
There was a German family once, two parents and their young son. Although the son was nearly four years old, he had never once spoken a word; indeed, he hardly made noise around the house at all, save for crying or bawling to show his displeasure, as infants often do. Naturally, this caused no small amount of grief and distress for his parents, who were concerned that there was something terribly wrong with their son. They took him to multiple psychiatrists and counselors, but none ever had any conclusive statement; most even said the boy was completely fine.
So, the mother, in an effort to get her son to speak, would feed him soup every night, and as she did so, she would talk to him, trying to get him to join in on the conversation. She would talk about their family, the news, the weather, anything that was going on in their lives, anything at all, to get her son to talk. This went on for years and years, with no visible change.
One night, however, during such a supper, the boy suddenly stopped his mother and said in a matter-of-fact voice: "Mother, the soup is cold."
His mother was understandably overwhelmed, embracing her son eagerly, sobbing, demanding to know, "Why? Why? Why have you never spoken all this time? Your father and I were so worried! Why have you only decided to speak now?"
The son simply replied, "Until now, the soup had been satisfactory."