Eels and reflection

This eel at Maryport Aquarium spent a lot of time confronting its own reflection. It must seem convincingly like a rival eel. One of the rules of reflection is that the image appears to be the same distance behind the the glass as the object is in front. This can be shown by drawing two reflected rays coming to the eye at slightly different angles. The brain can't cope with the idea that the light bent and thinks that the light has come in a straight line from a point behind the glass. If you extend the virtual rays backwards as dotted lines, they cross at a point a distance behind the glass that is equal to the object distance in front. see below