“We applied a red, yellow or black spot to a place on the necks of five magpies. The stickers could only be seen using a mirror. Then we gave the birds mirrors. The feel of the mark on their necks did not seem to alarm them. But when the birds with coloured neck spots caught a glimpse of themselves, they scratched at their necks—a clear indication that they recognised the image in the mirror as their own. Those who received a black sticker, invisible against the black neck feathers, did not react.