There is a puzzling asymmetry in English with respect to free relative clauses introduced by what and who, with the former (e.g. [What Glenn said] didn't make much sense) intuitively being much more acceptable than the latter (e.g. [Who Glenn married] didn't make much money). In this squib, we explore this degraded acceptability of who free relative clauses, and from the results of an experimental study we identify syntactic features of the sentence that influence the level of acceptability. We discuss the difficulty in finding an independently motivated solution to the puzzling asymmetry within current theories of syntax, semantic and processing. Finally, we touch on a broader theoretical question relating to the robust cross-linguistic process by which elements of the set of wh-words in a language are able to extend their function from introducing interrogative clauses to introducing other clausal constructions.