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[B]ut I was still cursed with my duality of purpose; and as the first edge of my penitence wore off, the lower side of me, so long indulged, so recently chained down, began to growl for licence. Not that I dreamed of resuscitating Hyde; . . . no, it was in my own person that I was once more tempted to trifle with my conscience. . . .
[However,] this brief condescension to my evil finally destroyed the balance of my soul. And yet I was not alarmed; the fall seemed natural, like a return to the old days before I had made discovery. It was a fine . . . day. . . . I sat in the sun on a bench; the animal within me licking the chops of memory; the spiritual side a little drowsed, promising subsequent penitence, but not yet moved to begin. After all, I reflected, I was like my neighbours; and then I smiled, comparing myself with other men, comparing my active goodwill with the lazy cruelty of their neglect. And at the very moment of that vainglorious thought, a qualm came over me, a horrid nausea and the most deadly shuddering. . . . I began to be aware of a change in the temper of my thoughts, a greater boldness, a contempt of danger, a solution of the bonds of obligation. I looked down; my clothes hung formlessly on my shrunken limbs; the hand that lay on my knee was corded and hairy. I was once more Edward Hyde.

These words appear in Jekyll’s confession, near the end of Chapter 10, and they mark the point at which Hyde finally and inalterably begins to dominate the Jekyll-Hyde relationship; Jekyll begins to transform into his darker self spontaneously, without the aid of his potion, and while wide awake. In the particular instance described in the passage, it only takes a single prideful thought to effect the transformation—although that thought comes on the heels of a Jekyll’s dip into his old, pre-Hyde debauchery. As elsewhere, the novel gives no details here of the exact sins involved in Jekyll’s “brief condescension to evil," and thus when he mentions “the animal within me licking the chops of memory," we are left to imagine what dark deeds Jekyll remembers. Again, the language of this passage emphasizes Jekyll’s dualistic theory of human nature, as he contrasts “the animal within me" to his “spiritual side." And the text deliberately presents Hyde’s body as animal-like, especially in the reference to a “corded and hairy" hand. In addition, Stevenson describes Jekyll’s longing as a “growl for licence," which, ironically, is reminiscent of animals communicating with each other. In a novel intentionally devoid of billowy language and concerned more with providing a record than with developing verbal description, Jekyll can be most vocally expressive of his desires when he longs to transform into Hyde. As Hyde, he loses the conscious abilities to form language completely, falling victim to the instincts within and losing the ability to recall exactly what is happening. The above description implies that Jekyll, in becoming Hyde, is regressing into the primitive and coming closer to the violent, amoral world of animals.