He first drilled some small holes in the wall, and then used an instrument to examine inside the wall itself. As expected, mud walls are behind the bricks, and they hold a lot of moisture. It's no mystery then why the murals were flaking off.
他先在牆邊挖好小洞，再利用內視鏡儀器勘察牆內：紅磚之後果然有泥土，而且像手拉坯一樣層層卷曲，可見潮濕程度之深，這也解開了外部壁畫剝落的謎底。