A chap sees a couple of workers out of his window and watches them for a while. The first guy digs a hole, then the other guy comes along and fills the hole in. They do this every 10 metres or so. After a while the chap can't watch any longer, and he goes to ask them what they are doing. "Oh," says the first guy. "We're from Herts Highways. There's usually three of us, but the lass who puts the tree in the hole called in sick this morning!"