Some bird species, such as the great-crested grebe (pictured), hunt underwater for fish and have red eyes. The red colouring is presumably beneficial to these diving birds, but in what way? If it does provide an advantage, why have other birds with similar habits not evolved red eyes?

Ian McKechnie, Weybridge, Surrey, UK

In countless films I've seen scuba divers communicating with one another over radio and yet I understand that water absorbs radio waves so how does this work? Or is it just a Hollywood myth?

Simon Forbes

Hove

During a recent lecture on the use of confocal microscopes, we were told that red light penetrates further into tissue than blue and green light.   This was demonstrated by the fact that a red laser is still visible when shone through a finger, but a green one isn’t.   This contradicts the loss of red light that is observed as you descend underwater; everything appears blue at depth when scuba diving.   Why is this?

However tight I fasten my swimming goggles they always end up round my neck after I dive in. This never seems to happen to Olympic swimmers. Why not?

Francis Melo, Birmingham, UK