mystify

verb

1. (transitive)To thoroughly confuse, befuddle, or bewilder.

   “Solar eclipses continued to mystify ancient humans for thousands of years.”

   “I had occasion […] to make a somewhat long business trip to Chicago, and on my return […] I found Farrar awaiting me in the railway station. He smiled his wonted fraction by way of greeting, […], and finally leading me to his buggy, turned and drove out of town. I was completely mystified at such an unusual proceeding.”