What does this line mean from Beowulf? "The monster's thoughts were as quick as his greed or his claws."

In Beowulf, the author is trying to present the listeners with the idea that this monster is something different from all the other monsters they have ever met, be they wolves, snakes or sharks. This monster is "other-worldy" and has something of the supernatural about it. This is because the cleverer and faster the monster then the cleverer and faster the "hero" who manages to vanquish him - in this case Beowulf. The worse the monster he overcomes the greater hero he is in the view of the listeners to the tale.

So, not only is this monster ruthlessly blood-thirsty he is almost impossible to outwit because he has brains as well as brawn. With lightning speed his mind is calculating his next move in the struggle just as Beowulf grapples with the last.As fast as his greedy claws are tearing, his next plan is racing. Beowulf must "face the monster" by "fighting fire with fire" as our modern saying goes.