우유갑은 왜 개봉하는 방향이 정해져 있을까?

<a href='http://cafe.daum.net/subdued20club' target='_blank'><img src='https://t1.daumcdn.net/cfile/cafe/2176E04958F1FBE032' class='txc-image ' /></a>출처 : 여성시대 마지심슨, 유튜브 사물궁이 잡학지식(https://youtu.be/20FjMw8vXG4) <img src='https://t1.daumcdn.net/cafeattach/1IHuH/2cd0e39b0c7f89890078c09108e76ab96af5b2dd' class='txc-image already_attached_image' /> <img src='https://t1.daumcdn.net/cafeattach/1IHuH/3d348b86211422c33a4939ce0954cdf5953d4d35' class='txc-image already_attached_image' /><img src='https://t1.daumcdn.net/cafeattach/1IHuH/78326e2633ae03e85b6561c5f6a9772a62d23b47' class='txc-image already_attached_image' /><img src='https://t1.daumcdn.net/cafeattach/1IHuH/6c131bb9d9c6cce0adbfa2772d659699b51561df' class='txc-image already_attached_image' /><img src='https://t1.daumcdn.net/cafeattach/1IHuH/d128dfe4eb69675b3b5f845a6c4fa3bd0e3e2945' class='txc-image already_attached_image' /><img src='https://t1.daumcdn.net/cafeattach/1IHuH/5a27d2e91394e0aafb1530ff01cc59d7bbada21f' class='txc-image already_attached_image' /><img src='https://t1.daumcdn.net/cafeattach/1IHuH/9c0a626eae736946a60886cb0de24f900af982e1' class='txc-image already_attached_image' /><img src='https://t1.daumcdn.net/cafeattach/1IHuH/a44691d208978bdf1f9cb0868bd60885ccd90772' class='txc-image already_attached_image' /><img src='https://t1.daumcdn.net/cafeattach/1IHuH/94307d472348abe1a1ac273e2119ad39eb2d7cf8' class='txc-image already_attached_image' /><img src='https://t1.daumcdn.net/cafeattach/1IHuH/37c71f09e24c9b89bf7cfc188f437568907070a8' class='txc-image already_attached_image' /><img src='https://t1.daumcdn.net/cafeattach/1IHuH/bbe3f1ebedff74cbb840822c991e7d308ec63f79' class='txc-image already_attached_image' /><img src='https://t1.daumcdn.net/cafeattach/1IHuH/3313bf3ad8b6dba89dd6dfb6a55a567ccc80309c' class='txc-image already_attached_image' /><img src='https://t1.daumcdn.net/cafeattach/1IHuH/072ff0faf753f335e2f25e6936e66e3fbbb1ada4' class='txc-image already_attached_image' /><img src='https://t1.daumcdn.net/cafeattach/1IHuH/78dfc04175c9e6960a91e5d65601c00005457627' class='txc-image already_attached_image' /><img src='https://t1.daumcdn.net/cafeattach/1IHuH/408247c7ce6151c318a9d46b61991dc0a8842299' class='txc-image already_attached_image' /><img src='https://t1.daumcdn.net/cafeattach/1IHuH/d394c01e830095f7c45a7fc9b0de47c3344f94e0' class='txc-image already_attached_image' /><img src='https://t1.daumcdn.net/cafeattach/1IHuH/67228c3ac4614c809a478f643bce8ea845789ad8' class='txc-image already_attached_image' /><img src='https://t1.daumcdn.net/cafeattach/1IHuH/10e6fad0e21068ab74f9107b2b2cfccae96ccf6d' class='txc-image already_attached_image' />