It seemed like his terror had taken on a physical form and was virtually making it impossible for him to move his legs. It wasn't like he didn't want to move. He was consciously making serious attempts to move backwards.
However, with each passing moment, it appeared that he had completely lost control of his legs. Zavier was appalled! What could he do?! The lady's eyes were still persistently scanning her surrounding. And any second now, it was very likely that her eyes would land on the unfortunate Zavier. If he wasn't trying so hard to move right now, Zavier would have probably passed out from mental exhaustion and shame. That would have been significantly better than trying to endure this shame and fear!