BT BM 84b(32) :אשכחוה לעכנא דהדרא ליה למערתא אמרי לה עכנא עכנא פתחי פיך ויכנס בן אצל אביו‏ : when they found that a snake had encircled the (burial) cave, they said to him [a freq. repeated passage with vars.]
See the entire entry for ˁeḵēn, ˁaḵnā n.f. viper