"A worm or mollusc that is injured, and perhaps writhing, may be feeling pain but could be showing an automatic response. The change in scientific thinking is that the weight of evidence for some of these animals now indicates that they may be feeling pain [...] Some aspects of the pain system exist in leeches, insects, snails, and swimming sea-slugs. However, we cannot be sure that these animals feel pain, or that they do not feel pain [...] There is a case for some degree of protection for spiders, gastropods and insects."