http://sfglobe.com/?id=829
On the OTHER hand, it requires you to either have a lot of plastic bottles, or to wash them afterwards.
On the subject of eggs...
The females of superb fairy-wren (Malurus cyaneus) start singing to their unhatched eggs in order to teach the embryo a “password,” a single unique note, which nestlings must later incorporate into their begging calls in order to get fed.
http://scitechdaily.com/eggs-of-superb-fairy-wren-learn-before-hatching/
On the OTHER hand, it requires you to either have a lot of plastic bottles, or to wash them afterwards.
On the subject of eggs...
The females of superb fairy-wren (Malurus cyaneus) start singing to their unhatched eggs in order to teach the embryo a “password,” a single unique note, which nestlings must later incorporate into their begging calls in order to get fed.
http://scitechdaily.com/eggs-of-superb-fairy-wren-learn-before-hatching/