‘CHILDREN, DID YOU ever try to define the difference between an animal and a vegetable?’ asks the freethinker and writer Elmina Slenker in her 1887 almanac for ‘little folk’. ‘It is easy to tell a cow from a tree, or a man from a potato. But when you take some of the lower forms of life and compare them, you will not find so much difference.’ Slenker gives her young readers the example of the plasmodial slime mould Fuligo septica, a bright-yellow unicellular organism born from a spore, which throbs and creeps over rotting tree trunks and leaf litter in its search for nutrients. Dividing itself, fusing with compatible amoeba it encounters and stretching upwards of two feet in length, the plasmodium will eventually fruit and burst into spores that start the cycle again. Slenker describes this organism as a ‘fungus plant’, which, ‘when placed under certain conditions, will change into an animal’ – a calmly scientific description of a folkloric wonder.

Slime mould (which is actually neither animal nor vegetable, nor even mould nor fungus, but an Amoebozoa) is one of the murky epistemological border dwellers that broke the two-kingdom system for classifying living things. In Western culture, writes theorist Jeffrey Jerome Cohen, these fissures in the classificatory ‘order of things’ have habitually spawned monsters. The compound living-dead flesh of Frankenstein’s creature; the wolf-rat-humanoid form of Dracula; the bivalve-reptilian Xenomorph – these monsters are ‘disturbing hybrids whose externally incoherent bodies resist attempts to include them in any systematic structuration’.