Previous research comparing communicative to non-communicative computer-mediated tasks requiring output production found an advantage in L2 vocabulary learning efficiency in favor of the communicative task (Hughes, 2023). The present study analyzes the chat data from Hughes (2023) to determine what features of interaction may have contributed to the advantage in L2 learning efficiency. Notable features included the negotiation of meaning, paraphrasing keywords, and context-elaborative question formulation. Of these, elaborative question formulation was found to correlate most strongly with L2 learning efficiency. Furthermore, a significant difference in L2 learning efficiency was found between participants who had engaged in elaborative question formulation and those who had not in favor of those who had. Learners who had engaged in elaborative question formulation also demonstrated a marginally significant advantage in L2 learning efficiency over participants who completed the non-communicative task. The implications of these results are discussed from a cognitivist perspective.