http://phys.org/news/2013-10-canny-crows-tools.html
In my chapter "Clever Corvids" i documented a range of experiments, to book publication date, that tested tool use in crows - particularly New Caledonia crows. Their use of hooked tools is a feature of their foraging and they have a very particular way of fashioning the hook tool from foliage by judicious snipping of V-branches in twigs. But debate has see-sawed ever since as to whether the crows learn this tool fashioning and use by trial-and-error, or whether they have some mental picture of
what they are doing - whether they understand it. This interesting article, about the work of a research group from the University of St. Andrews favours the latter, more profoundly interesting, interpretation of what crow tool use mentally represents. As the lead author, James St. Clair, is quoted as saying: ""We still can't say whether New Caledonian crows actually 'understand' how their tools function. But of course, this is also true of many humans I know!"