gnawing

对未来的担忧一直折磨着他。

The worry about the future kept ___gnawing at him.

松鼠不停地啃咬树皮寻找食物。

The squirrel keeps ___gnawing the bark to find food.

对考试的担忧一直折磨着他。

The worry about the exam was ___gnawing at him all day.