The custom of swinging a chicken over one’s head on the eve of Yom Kippur, slaughtering it, and giving it to a poor family was once widespread among Jews. Now this exotic ritual is primarily relegated to the ultra-Orthodox. But even despite its former prevalence, it is nowhere mentioned in the Talmud, and was condemned by some medieval and modern rabbis. Shlomo Brody recalls:
When I was a sixteen-year-old yeshiva boy studying in Jerusalem, my friends invited me to go with them to “shlug kaparos” on the day before Yom Kippur. Though I grew up Orthodox, in Houston, I was not familiar with the term (which translates loosely as “beat the atonements”), but I was quickly off to the Mahane Yehuda market, where we muttered a quick prayer as a shohet [kosher slaughterer] waved a chicken over our heads. He slaughtered the animal and threw it into an overflowing bin destined for the poor. . . . As I recited Kol Nidre that evening, murmurs of angst crept into my head: Was that really a holy act? As it turns out, many commentators, both medieval and modern, have called it a grave mistake.
Read more on Tablet: http://www.tabletmag.com/scroll/185741/a-brief-history-of-a-fowl-custom