There is presently a lively debate in second language (L2) acquisition research as to whether (adult) learners can acquire linguistic phenomena located at the interface between syntax and other modules, such as semantics, pragmatics, and lexical semantics, in contrast to phenomena that are purely syntactic in nature. For some researchers, the interface is precisely the place where fossilization occurs and the source of nonconvergence in L2 speakers. In this article we focus on the acquisition of the morphosyntax-semantics interface by examining the acquisition of mood in Spanish relative clauses by native speakers (NSs) of English. In particular, we focus on the contrast illustrated by "Busco unas tijeras que corten" "I am looking for scissors that cut-SUBJ" versus "Busco unas tijeras que cortan" "I am looking for scissors that cut-IND." When the indicative is used, there is a specific pair of scissors that the speaker is looking for. With the subjunctive, any pair of scissors will do, as long as it satisfies the condition expressed by the relative clause; the determiner phrase is nonspecific. In other words, we are dealing not with ungrammaticality, as both moods are possible in these contexts, but rather with differences in interpretation. General results showed that the learners could appropriately select the expected mood. We also saw that performance was not uniform across the various conditions tested. However, variability is not solely a product of L2 acquisition; we show it can be found in NSs as well.