Practical arguments or enthymemes are interactive. Speakers typically set out some premises of their own while asking listeners to supply others already known or believed. Such arguments are likely to fail if a speaker leaves out key premises that listeners cannot or will not covertly fill in, or if a speaker attributes premises to listeners that do not faithfully reflect their beliefs. Here I examine this challenge as it applies to mixed enthymemes, arguments that speak across different domains of inquiry, in this instance those of science and religion. Because such arguments turn upon religious as well as scientific premises, they can only succeed if their religious premises are consistent with what is taught in the faith traditions of students. Here I explore how this challenge arises in three enthymemes from the University of California Museum of Paleontology's website "Understanding Science."