To answer the question about the work of the masters. Most of the amimals are far from perfect. A good example of imperfection is the work of Napoleone Martinuzzi. The faces of his animals tend to be well done, but the tails look like a child was playing with play-dough. Even the greatest masters had imperfections in their work. (Sometimes it seems to me that the greater the name, the more the imperfections back in the old Murano days.)
Eyes that are made by cutting bits of cane, then melting in the furnace often have pulls and inconsistencies. Some of the birds end up with eyes in different places on the face, making them look crazy. Tails are often made by flattening a pieces of glass, then snipping, shaping and reheating. It is okay for them to show evidence of the treatment. Many birds have squared off feathers. Some have feathers that are cut unevenly. All of these things are okay, though it is always good to try to find birds that have the most attractive features.
IOW's bird is a good one. Tooling marks are completely okay with art glass as long as they don't mar the beauty of the piece. There are certain fields that are important for viewing, so one wouldn't want a large tooling mark there, but in out of the way places, they are expected and acceptable.