Rhetoric has been characterized throughout its history as an art that must conceal itself to succeed. Two arenas where rhetoric has been most successfully concealed are those of science and technology. This essay explores the general conditions and justifications for the concealment of rhetoric, finding that four principles appear repeatedly in the ancient tradition: suspicion, spontaneity, sincerity, and mimesis. In response, rhetorical art has developed strategies to allay suspicion, create the impression of spontaneity and sincerity, and emphasize the direct mimetic power of language, strategies that themselves must be concealed. Two examples drawn from the rhetoric of science and technology, specifically the discourse of risk analysis, illustrate the operation of rhetorical concealment. The first example, a foundational 1969 scientific article by engineer Chauncey Starr, relies on an unacknowledged rhetoric of pathos; the second, the 1975 Reactor Safety Study by the U.S. Nuclear Regulatory Commission, relies on an appeal to ethos, disguised as technical expertise.