Why will there be thorns in the castles?
Rashi: Thorns and bushes normally sprout in ruins. Kimush and Cho'ach are kinds of thorns.
Malbim: At a time of Shalom, they dwell in the castle. At a time of war, they dwell in the fortification. Now, both of them will be [desolate, and] full of thorns.
What is "Naveh Sanim"?
Rashi: It is a Midbar, where Sanim are normally found. It is an evil beast.
Malbim: Naveh is a place for flocks to lie. Due to the weeds, i.e. thorns, it will become a place of Sanim.
What is "Chatzir"?
Radak: This is like Chatzer with a Tzeirei. Targum Yonasan says, a place [for ostriches].
Malbim: It is grass. It will be for ostriches, which eat even broken glass, and also thorns.
