Previous studies on co-teaching have reported how a native English-speaking (NES) teacher and a non-native English-speaking (NNS) teacher jointly instruct students in their English language classes, yet little is known about their speech behaviour in teaching interpreting as a cross-language, cross-culture task. To bridge the gap, the study recorded the process of co-teaching by one NNS and one NES in a ten-week Chinese-English interpretation course. Using the initiation-response-follow-up talk analysis as its framework, it found that each teacher alternatively prompted and evaluated students in their class talk, with the NES treating and suggesting students' English use and the NNS demonstrating and diagnosing students' translation pitfalls. Interviews with the teachers and students revealed that both teachers served as quality inspectors and cultural advisors with complementary perspectives and knowledge. However, a negative side of co-teaching was that the increased teacher-teacher interactions could stifle students' active thinking, turning them into a kind of passive talk-show listeners waiting to be entertained. Based on those findings, the paper suggested some revised interaction patterns for co-teaching.