Zalman Schachter-Shalomi told a group that there was a magic song the Baal Shem Tov once taught his students, saying if they sang it after his death, he himself would be there among them. 
A listener asked Zalman, “So, what is the song?”
“Ah,” he had to confess, “I don’t know the actual words or tune.”
“Oy,” lamented his questioner, “Such a good gun and no bullets!”