Our sense of smell is binaral.

When different images are presented to each of our two eyes, or different sounds to each of our two ears, our perception usually switches back and forth between the two alternatives. Now Zhou and Chen have found that the same applies to two odors separately presented to each nostril. This binaral rivalry involves both cortical and peripheral (olfactory receptor) adaptations. (If one of two odors is first presented to a nostril, and then after a brief interval it is again presented to the nostril while a second odor of equal initial power is presented to the other nostril, the second odor is predominantly sensed.)