BT Hag 11b(30) :תרי כי יתבי קמי רבה, חד שקיל וטרי בהדי רבה, אידך צלי אודניה לגמרא‏ : when two are sitting before the teacher, one is discussing with the teacher while the other bends his ear to the teaching
See the entire entry for ṭry vb. to thrust at; throw at