We suggest a novel theoretical analysis of what is known as the reactive what-x construction. This construction, which has recently been noticed and described in Põldvere & Paradis (2019, 2020), has primarily clarificational properties and requires the presence of an antecedent in the preceding context. We begin by summarizing its syntactic properties and main functions, based on data drawn from the London–Lund Corpora of spoken British English, and then address a pattern that has escaped notice thus far, i.e. that the majority of the instances of this construction feature a type of ellipsis known as fragments. Departing from the analysis articulated in Põldvere & Paradis (2020), we present one that captures the elliptical properties of the reactive what-x construction by assimilating it to two classes of fragments: those serving as reprise utterances and those serving as direct utterances. Our analysis relies on Ginzburg & Sag's (2000) detailed analysis of reprise and direct fragments couched within a non-sententialist approach to ellipsis. This allows us to analyze the reactive what-x construction as a type of an in-situ interrogative clause whose elliptical properties are licensed by a version of the constraint Ginzburg & Sag (2000) use to license fragments.