One passage from Frankenstein that illustrates the theme of "the danger of pushing beyond natural boundaries in science" is:
"I saw—with shut eyes, but acute mental vision,—I saw the pale student of unhallowed arts kneeling beside the thing he had put together. I saw the hideous phantasm of a man stretched out, and then, on the working of some powerful engine, show signs of life, and stir with an uneasy, half-vital motion. Frightful must it be; for supremely frightful would be the effect of any human endeavor to mock the stupendous mechanism of the Creator of the world."
This passage describes the moment when Victor Frankenstein brings his creation to life, and the horror that he feels when he realizes the full extent of what he has done. He describes the "pale student of unhallowed arts" as pushing beyond the natural boundaries of science, attempting to create life itself. The passage suggests that this kind of scientific pursuit is dangerous and even "supremely frightful," as it amounts to an attempt to "mock the stupendous mechanism of the Creator of the world." This idea is central to the novel's exploration of the consequences of scientific ambition, and it underscores the dangers that can arise when humans seek to play god.