The fear behaviors induced by magnetothermal treatment in freely moving mice administered the optimal dose of FVIOs were systematically investigated using in situ video recording and further analysis according to standard protocols. Upon AMF exposure, the FVIO-stimulated mice showed freezing of gait, with locomotion inhibited in place and all four paws locked, although the mice were free to move their heads (Figure 6a). These behaviors reflected the innate anxiety and fear responses of the mice. The tracked positions and total distances traveled are displayed in Fig. 6 (b and c). The mice displayed active locomotion within the arena (coil) before stimulation. During stimulation, the mice preferentially remained frozen, showing an apparent decrease in ambulatory activities (movie S3, Supporting Information). The percentage of freezing time in the FVIO treatment mice after the application of an AMF was 79.58 ± 24.54%, which was 2.56-fold greater than that among the FVIO-treated mice without AMF exposure (Figure 6d). Before and during stimulation, the mice also exhibited significant increase in the total number of freezing episodes (from 5 to 25), which is consistent with the significant decrease in average speed (from 2.3 cm/s to 0.2 cm/s), as shown in Fig. 6 (e and f).