1. The walls were decorated with mirrors, yellowed and spotted with age
2. the howling of a small child drowned the hububb of the hall.
A sensory detail is any detail that pertains to one of the five senses (sight, touch, hear, smell, taste). throughout this passage there are many descriptions that appeal to the sense of sight. These details do not have to be heavily detailed or long, just so long as they help to put an image in the reader's head. The first example does this. It not only tells you that there are mirrors on the walls, but also describes how they've aged.
The second example appeals to the sense of hearing. It describes the noise of the child down the hall in comparison to the typical noise of the hallway.