Normally a lion does not roar before he hunts since this would alter prey to his presence and cause it to flee. However, the image being conveyed here is perhaps suggestive of a warning growl which is uttered before a lion attacks or the sound that it makes just before and whilst it captures its prey. It may also be that the people of the ancient Near East understood the roar of a lion to indicate that he had found his prey and was about to attack (e.g. Psalm 104:21). Perhaps (in their understanding), the lion’s roar would cause prey to freeze, and thus make it easier for the lion to capture his prize.1
4 Does a lion roar in the forest, when he has no prey? Does a young lion cry out from his den, if he has taken nothing?