Talmud for Shabbat 184:6
ולאחריו ובא לו לאחריו תנאי היא דתניא [המוציא מעות בפונדתו ופיה למעלה חייב פיה למטה רבי יהודה מחייב וחכמים פוטרין אמר להן ר' יהודה אי אתם מודים בלאחריו ובא לו לאחריו שהוא חייב ואמרו לו ואי אתה מודה כלאחר ידו ורגלו שהוא פטור
IF ONE INTENDS TO CARRY OUT [AN OBJECT] IN FRONT OF HIM, BUT IT WORKS ROUND BEFORE HIM, HE IS NOT CULPABLE: hence [if he intends to carry it] behind him and it comes behind him, he is culpable. Then consider the second clause: BEHIND HIM, BUT IT WORKS ROUND BEFORE HIM, only then is he CULPABLE: hence [if he intends to carry it] behind him and it comes behind him, he is not culpable?<span class="x" onmousemove="('comment',' Presumably because such carriage is unnatural, as one cannot exercise a proper vigilance. ');"><sup>10</sup></span> — Said R. Eleazar: There is a contradiction: he who learnt the one did not learn the other. R. Ashi observed: But what is the difficulty: Perhaps he leads to a climax:<span class="x" onmousemove="('comment',' Lit., 'he states', 'it is unnecessary'. ');"><sup>11</sup></span>