«وَضَرَبَتِ الْبَلُّورَ بِالدُّرَرِ»
She struck crystal with pearls.
In this context, crystal evokes translucent fingers or the hand, while pearls represent white teeth. The same fingertip-biting action from the first verse now returns in the vocabulary of precious materials.
The physical action is the meeting of fingertips and teeth; crystal and pearls are the figurative language used to describe it. The line should not be read as a literal account of gemstones striking one another.