Research suggests that gestures influence cognitive processes, but the exact mechanism is not clear. Additionally, it has been shown that when a linguistic task (metaphor explanation) involves the right brain hemisphere, the left hand becomes more gesturally active. We hypothesized that gestures with a particular hand activate cognitive processes in the contra-lateral hemisphere. We examined whether gestures with the left hand enhance metaphoricity in verbal responses. Results showed participants produced more metaphoric explanations when instructed to produce gestures with their left hand as compared to the right hand or not gesture at all. In addition, we measured the mouth asymmetry during metaphorical speech to determine individual differences in right-hemisphere involvement in metaphor processing. The left-side mouth dominance, indicating stronger right-hemisphere involvement, positively correlated with the left-hand-over-right-hand advantage in gestural facilitation of metaphorical speech. We concluded that left-hand gestures enhance metaphorical thinking in the right hemisphere.