In lines 270-275 of Beowulf, Beowulf is addressing Hrothgar. Prior to line 270, Beowulf is providing Hrothgar his ancestral background. He wants Hrothgar to know that he is both a Geat and kin of Hygelac (his father). Hrothgar knew Beowulf's father, and Beowulf knows that this fact will insure Hrothgar's acceptance of him and his men.
Lines 270-275 illustrate the fact that Grendel has been heard of far and wide. The tales of Grendel, a "scathing monster," are renowned. Beowulf also states that his trip to the Danelands is because of this monster.
Given the limited nature of the lines, here are a couple suggestions about what one could draw.
-An image of Grendel.
-A picture of numerous men speaking about the "scathing monster" and passing the mental image of him by word of mouth (which also speaks to the oral tradition by which the epic was passed).