From all that has been discussed in the earlier chapters, it seems that nearly all the natural daylight we see is at least partially polarised. Polarisation is unavoidable because we never look directly at the sun and all the light that actually enters our eyes has been either reflected or scattered by something. It turns out that many animals are able to detect both the degree of linear polarisation and its direction, and they exploit this information in several ways. Such creatures include insects, crustacea, octopus and cuttlefish and some vertebrates but not, except in an insignificant way, ourselves and other mammals. Having already seen in this book what we are missing, it is pertinent to consider how other eyes respond to polarisation and why ours do not.