"Cursed is he who secretly strikes his fellowman" [Ki Tavo 27:24]
Rashi explains that this curse refers to one who speaks lashon hora - when someone speaks evil, he secretly "strikes" his fellowman.
The Chofetz Chaim was traveling in the company of a well-known rabbi on their way to performing a mitzvah.
After traveling for some time, they decided to rest at an inn.
The woman who owned the inn realized that her two new guests were highly esteemed rabbis, so she quickly set a table and offered them various delicacies.
When they had finished eating, she approached them and asked "How was the meal?"
"It was excellent!" remarked the Chofetz Chaim. "The food was delicious."
"And how did you enjoy the food?" asked the hostess to the other rabbi.
"The food" answered the rabbi, "was certainly adequate, but it could have used a bit more salt."
Their hostess cleared the table and entered the kitchen.
As soon as she left the room, the Chofetz Chaim turned to the rabbi and, with sorrow in his voice, said: "All my life, I have taken the utmost care not to speak or hear words of lashon hora. But now that I am in your company, you have caused me to falter - I am greatly distressed that I have made this trip. I am sure that this trip was not truly for the sake of a mitzvah, for it is impossible that one who has set out to perform a mitzvah should come to violate such a grave transgression!"
"But what did I say?" asked the rabbi. "I said the food was good. I just added that the food could have used a little salt."
"You have no idea," answered the Chofetz Chaim, "of the incredible power of one's words. In all likelihood, the cook is a poor widow who works in this inn to support her family. I am sure that because of your comment, the hostess will go to this poor widow and tell her that the guests are complaining about her cooking. The widow, in defense of her cooking, will deny that the guests have any grounds for complaints. At that point, the hostess will become incensed and shout at her "Do you think the distinguished guests are lying? You are the one who is the liar!" Ultimately, the hostess, in a fit of anger, will fire the poor unfortunate cook."
"Just look at how many sins you have committed with your words: (1) You spoke lashon hora; (2) you caused both the hostess and myself to hear lashon hora; (3) you caused the hostess to relate the words of lashon hora to the cook; (4) you caused the cook to lie in defense of her cooking; (5) you caused the cook terrible suffering."
"Surely you are exaggerating" said the rabbi to the Chofetz Chaim.
"Not in the least" responded the Chofetz Chaim. "Come with me and I'll show you."
The two rabbis entered the kitchen and were greeted with a sorry sight. The poor cook was standing with her head in her hands, sobbing.
The rabbi took one look at the widow, and immediately understood just how correct the Chofetz Chaim had been. He quickly made his way to the hostess and pleaded with her to forgive the cook and restore her to her position.
Source: Rabbi Yisrael Bronstein