At first, while the nest was shallow, only one could work at a time; and if Petro came back with his plaster before Eve had patted the last of hers into place, she would squeak at him in a fidgety though not fretful voice, as if saying, "Now, don't get in my way and bother me, dear." So he would have to fly about while he waited for her to go. The minute she was ready to be off, he would be slipping into her place; and this time she would give him a cosy little squeak of welcome, and he would reply, with his mouth full of plaster, in a quick and friendly way, as if he meant, "I'll build while you fetch more plaster, and we'd both better hurry, don't you think?" After worrying a bit about the best place to dump his hodful, he went to work. He opened his beak and, in the most matter-of-fact way, pushed out his lump of plaster with his tongue, on top of the nest wall. Then he braced his body firmly in the nest and began to use his trowel, which was his upper beak, pushing the fresh lump all smooth on the inside of the nest. Have you ever seen a dog poke with the top of his nose, until he got the dirt heaped over a bone which he had buried? Well, that's much the way Petro bunted his plaster smooth--rooted it into place with the top of his closed beak. He got his face dirty doing it, too, even the pretty pale feather crescent moon on his forehead. But that didn't matter. Trowels, if they do useful work, have to get dirty doing it, and Petro didn't stop because of that. If he had, his nest would have been as rough on the inside as it was outside, where a humpy little lump showed for each mouthful of plaster. Although Eve and Petro did not fly off to the plaster pit together, they did not go alone, for there was a whole colony of swallows building under the eaves of that same barn; and while some of them stayed and plastered, the rest flew forth for a fresh supply. They knew the place, every one of them; and swiftly over the meadow and over the marsh they flew, until they came to a pasture. There, near a spring where the cows had trampled the ground until it was oozy and the water stood in tiny pools in their hoof prints, the swallows stopped. They put down their beaks into the mud and gathered it in their mouths; and all the time they held their wings quivering up over their beautiful blue backs, like a flock of butterflies just alighting with their wings atremble. So their plaster pit was just a mud-puddle. Yes, that is all; only it had to be a particularly sticky kind of mud, which is called clay; for the walls of their homes were a sort of brick something like that the people made in Egypt years and years ago. And do you remember how the story goes that the folk in Pharaoh's day gathered straws to mix with the clay, so that their bricks would be stronger? Well, Eve and Petro didn't know that story, but they gathered fibres of slender roots and dead grass stems with their clay, which doubtless did their brick plaster no harm.