今日の英語： nip at someone's heels

For centuries, people have been on the move, needing to follow a food supply, in search of a better climate, or just because we wanted to know what's over that next hill.

So, if the moving bug is starting to nip at your heels, how do you know the time is right for you to pack up all your things and head in a different direction?
How can you be sure that you're making the right decision?
 Since our destination is usually a little foggy, we can never be 100% certain; however we can feel confident that our decision to move is based on clear objectives and not just because we think the grass might be greener.
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nip at someone's heels
すぐそばまで追い上げる、じりじりと追い上げる、ジワジワと攻撃する、領域を侵食する
He has been nipping at Smith's heels the entire season, only a few points away from the top position.
彼は今シーズン中ずっとスミスを追い上げており、トップの座にあと数ポイントだ。