An idiom meaning one's eyes dart around (due to nervousness, guilt, or uncertainty); to have a shifty or unsettled gaze.
面接で彼は質問されると目が泳いで、落ち着いて答えられなかった。
In the interview, when asked questions he looked shifty and couldn't answer calmly.
彼女は罪を認めさせられそうになると目が泳いだ。
When it seemed she might be forced to admit guilt, her eyes started to dart around.
プレゼン中に資料の内容を忘れてしまい、目が泳いでしまった。
I forgot part of the material during the presentation and my eyes started darting around.