It is often argued that the general propriety of challenging an assertion with ‘How do you know?’ counts as evidence for the Knowledge Norm of Assertion (KNA). Part of the argument is that this challenge seems to directly challenge whether a speaker knows what she asserts. In this article I argue for a re-interpretation of the data, the upshot of which is that we need not interpret ‘How do you know?’ as directly challenging a speaker's knowledge; instead, it's better understood as challenging a speaker's reasons. Consequently, I argue that reasons-based norms can equally well explain this data.