Stringing Christmas Lights

Today my father and I strung Christmas lights from the eaves. Like most household projects it was supposed to take an hour's time, but it lasted for most of the afternoon. By the time we were done my hand was badly scratched, and a dozen bulbs were broken and replaced. At last the lights were up. Mother came outside to witness while Dad did the honors. Two plugs were brought together and most of the lights came instantly aglow... but not all of them. There were two significant stretches where not a single light was lit.

After a pause my mother asked, "Well, what should we do?"

"I don't know," dad replied, "but the only time anyone would ever notice is at night."