The present study evaluates the effects of incompatible verbal behavior when engaging in the Wisconsin Card Sorting Test (WCST). The WCST is a complex task that requires participants to match stimulus cards based on self-generated rules. After a varying number of trials, the rule changes and the participant will have to self-generate a new rule. Verbal behavior, specifically joint control, is likely involved in rule-following. Seven participants took part in this study. Participants engaged in the WCST either silently or while performing a putatively incompatible behavior, counting backward from 100 to 0. Results suggest joint control might be involved as when participants engaged in the incompatible behavior their performance was affected in terms of lower accuracy and longer reaction times compared to the silent baseline.