مُسْتَشْزِرَات
Raised or projecting upward; in the poem, it describes locks of hair.
This is the textbook's principal example of a difficult sound sequence. The poet describes hair, and this particular word is presented as burdensome to pronounce. The objection is directed at its phonetic shape, not at the basic meaning being conveyed.
The commentary explains the upward sweep or spread of the hair. Understanding the image does not itself remove the word-level articulatory problem.