A Chinese businessman operating out of south China suffers a string of robberies. He calls up his associate in Israel and asks him if he ever had a problem with robberies.
"Not really," replies the Israeli. "We have this thing we put on the doorpost called a mezuzah and it protects our homes from harm."
"Send me one," begs the Chinese guy, "I'm desperate for a solution."
A few weeks later, the Israeli gets his mezuzah back in the mail. He calls up his Chinese friend. "Nu," he asks him. "The mezuzah didn't work? You were robbed again?"
"No, no," the Chinese guy assures him, "no robberies."
"So why did you send it back?"
The Chinese guy sighs. "I dunno," he says. "Ever since I hung it up, the doorbell doesn't stop ringing. Each time a different man standing there, saying the same thing: 'Tzedakah please!'"