grasps at

The demon cannot rationalize why this is so; it only sees a target and grasps at the opportunity.

而这些恶魔却并不能理性地思考这是为什么，它们只知道立刻抓住这个机会并侵占目标。

A drowning man clutches (or grasps) at straws

（快要溺死的人连稻草也要去抓）。