How does John Wyndham use imagery in The Day of the Triffids?

Example of Imagery:

When it walked it moved rather like a man on crutches. two of the blunt “legs” slid forward, then the whole thing lurched as the rear… At each step the long stem whipped violently back and forth… Nevertheless, ungainly though it looked, it was contriving to cover the ground at something like an average walking pace.” (pg. 27)