"‘They know—it's too monstrous: they know, they know!’
‘And what on earth—?’ I felt her incredulity as she held me.
‘Why, all that we know—and heaven knows what else besides!’ Then, as she released me, I made it out to her, made it out perhaps only now with full coherency even to myself. ‘Two hours ago, in the garden’—I could scarce articulate—'Flora saw!’"

The Turn of the Screw is a story full of vagueness. There are many details hinted at by characters that are never expanded upon or specified. The ambiguity of these allusions suggests they concern subjects so forbidden or taboo the characters can’t even speak of them. This conversation between the governess and Mrs. Grose in Chapter 7 exemplifies the governess’s preoccupation with a subject so “monstrous” she can’t name it. It’s indicated that whatever knowledge she suspects the children have acquired by spending time with Peter Quint and Miss Jessel is strictly for adults—they know “all that we know,” after all, with “we” referring to the governess herself and Mrs. Grose. Even more terrifying than that, however, is the prospect of the children possessing knowledge that exceeds that of the governess, as she explains when she adds, “—and heaven knows what else besides!”

“‘Quint was much too free.’
This gave me, straight from my vision of his face—such a face!—a sudden sickness of disgust. ‘Too free with my boy?’
‘Too free with everyone!’”

This exchange between Mrs. Grose and the governess in Chapter 6 allows the governess to begin making inferences about Miles’s relationship with Peter Quint, and to link the child’s bad behavior to the former valet. What knowledge Quint may or may not have imparted to Miles isn’t stated, but the governess begins to suspect something passed between the two, leading to Miles’s corruption.

“What it was most impossible to get rid of was the cruel idea that, whatever I had seen, Miles and Flora saw more—things terrible and unguessable and that sprang from dreadful passages of intercourse in the past. Such things naturally left on the surface, for the time, a chill which we vociferously denied that we felt…”

This quote from Chapter 13 captures the sense of terror and unease that plagues the governess, knowing that Miles and Flora have seen horrible things beyond her understanding. Once again, she doesn’t name or specify, but the fact that whatever they have seen must surely be “terrible and unguessable” is perhaps more frightening than any specific image Henry James could conjure.