Research on joint action has been taken to suggest that actors automatically co-represent the tasks and/or actions of co-actors. However, recent findings on the joint Simon effect have provided evidence for a nonsocial account, which renders automatic co-representation unlikely. In the present study, we aimed to test whether a nonsocial account is also feasible for the joint version of the flanker task. In particular, we manipulated the social nature of the "co-actor" who could be another human or a Japanese waving cat. Contrary to the social interpretation of the joint flanker effect, the results demonstrated a "joint" flanker effect, irrespective of whether participants shared the task with another person or with the Japanese waving cat.