Prendick and Montgomery start out as foils, but by the end of the novel their differences have largely disappeared. In Chapter 19, Montgomery points out the futility of Prendick's attempts to distinguish himself from both Montgomery and the Beast Folk:
“Very well,” said I, and stood aside, half-minded to fall upon him as he put his hand upon the latch, but deterred by the thought of my useless arm. “You’ve made a beast of yourself. To the beasts you may go.”
"[...] You’re a solemn prig, Prendick, a silly ass! You’re always fearing and fancying. We’re on the edge of things. I’m bound to cut my throat to-morrow. I’m going to have a damned good bank holiday to-night.”
In this scene, Montgomery is taking alcohol to M'ling. Prendick's longtime refusal to partake of alcohol represents, to him, his humanity prevailing over a base animal appetite for drunkenness. Abstaining from alcohol helps him keep a clear line between himself and the Beast Folk. Montgomery does not resist this appetite. He has "made a beast of himself."
Yet Prendick sees a difference between Montgomery's drunkenness and the drunkenness of Beast Folk. Alcohol is part of human society, and Prendick worries that the Beast Folk will not be able to keep their reaction to it in check the way a full human can. This worry is tinged with racism: Montgomery claims that M'ling "takes his alcohol like a Christian." European Christians often introduced alcohol to the societies they colonized, and it could have devastating effects on populations not used to consuming it. To handle alcohol "like a Christian" is to be able to metabolize it more like white colonizers than the populations they colonized. Prendick sees Montgomery as someone who has surrendered to his appetite for drunkenness but who can drink alcohol and still maintain some sense of law and order. He sees M'ling as someone who will lose all sense of law and order if he drinks alcohol.
Montgomery makes the point that "we're on the edge of things." He believes that Prendick's distinction between humans and animals is "priggish," or prudish and old-fashioned, given the circumstances. They are in a survival situation, so Montgomery and Prendick may as well allow themselves to be animals. By the end of the novel, trying to survive convinces Prendick that all humans, himself included, are much more like Montgomery than they realize. Montgomery is only unique in that he openly lives "on the edge" of human and animal existence. In fact, Prendick lives on this same edge, and so does M'ling. As the use of Prendick and Montgomery as foils gradually makes clear, there is very little stopping any human from throwing law and order out the window.
