They said, "If you send away the ark of the God of Israel, don't send it empty; but by all means return him a trespass-offering: then you shall be healed, and it shall be known to you why his hand is not removed from you."
"Milch" cows (1 Samuel 6:7; 1 Samuel 6:10) are cows that are still nursing their calves. It would be very unusual for nursing cows to leave their young and head for a town some 10 miles away. Indeed the Philistines regarded this behavior as miraculous and indicative that Yahweh had been punishing them.