I get two bottles of milk delivered to my house each day. One, containing whole milk, ha a silver foil top, whereas the other, containing semi-skimmed milk, has a silver top overprinted with red stripes. Based on observation over several years, the local magpie population will often try to peck at and remove the striped top but hardly ever attack the plain silver foil top Have other readers observed magpies or other birds beings so discerning and is there a scientific explanation for it?tbcThe Last Word explores the science of everyday things. Both the questions and the answers are provided by the smartest people we know – you, the New Scientist users. You can post your answers in the comments under each blog post. Please keep on topic and concise.You can browse recent Last Word questions by topic: human body, domestic science, planet Earth, weather, Animals, plants, Environment, Technology and Transport. Or you can search all of the Last Word back to 1994 by adding your keywords to this search. You can also buy the latest book (US or UK).You can't post questions online just yet. For questions, and answers you want to send direct to us, please use email (lastword at newscientist.com, or use the button above right), post (Last Word, New Scientist, 84 Theobald’s Road, London, WC1X 8NS, UK), or even fax (+44 20 7611 1280).The writers of all answers published in our print magazine receive a cheque for £25 (or the US$ equivalent), so we'll need your email address to contact you. We reserve the right to edit for clarity and style. Reed Business Information Ltd reserves all rights to reuse the question and answer material submitted in any medium or format.