Because eggs will rot if the contents are left inside, they must be "blown" to remove the contents. Although collectors will take eggs at all stages of incubation, freshly laid eggs are much easier to blow, usually through a small, inconspicuous hole drilled with a specialized drill through the side of the eggshell. Egg blowing is also done with domestic bird's eggs for the hobby of egg decorating. Numerous books, and at one point a journal, have been published on egg collecting and identification: