Sense
Magnetoception (or magnetoreception) is the ability to detect the direction one is facing based on the Earth's magnetic field. Directional awareness is most commonly observed in birds, which rely on their magnetic sense to navigate during migration. It has also been observed in insects such as bees. Cattle make use of magnetoception to align themselves in a north-south direction. Magnetotactic bacteria build miniature magnets inside themselves and use them to determine their orientation relative to the Earth's magnetic field.
Spin chemistry
Because the Zeeman Interaction is a function of magnetic field and Larmor frequency, it can be obstructed or amplified by altering the external magnetic or the Larmor frequency with experimental instruments that generate oscillating fields. This is interesting because migratory birds lose their navigational abilities in similar conditions where the Zeeman interaction is obstructed in radical-pairs, and researchers can control these conditions to probe the importance of Zeeman Interactions in Magnetoreception, implicating the presence of a radical-pair mechanism.