Cold Water

A boy went to his grandfather's house for a week. On the first night at dinner he found a thick, slimy goo on his plate, so he said to his grandfather "Grandpa is this plate clean?"
"As clean as cold water can get them." his grandfather answered. This went on for the rest of the week. On the last day when the boy was leaving the dog wouldn't let him through. So he said "Grandpa your dog won't let me through." His grandfather replied "Cold Water go lie down"