This article adopts the methods of conversation analysis to track the details of three English as a foreign language novice teachers' language alternation practices in a Vietnamese tertiary context. The analyses focused on teacher instruction-giving in the pre-entry and main instructional phases of lessons. Findings show that language alternation was an important tool in the organisation of the teachers' instructional talk to pursue student response and establish understanding. A key and recurring finding is that teachers started their instructions or pre-instructions in English but quickly switched to Vietnamese, often without providing any wait time for students to respond. The study also provides empirical evidence for students' reticence but suggests that this may well be the result of teachers' own instructional practices.