Kerisus 11a: It is an expression of change. We learn from here to Shifchah Charufah (Hei and Ches are interchangeable). If she was a virgin (before relations with him) he is exempt - "v'Hi Shifchah Necherefes l'Ish".

Rashi: It is wheat crushed in a mortar.

Rashi: It is a pestle.

Malbim: An Evvil is not refined and his impurities do not depart from him even via great afflictions. An Evvil has doubts about the laws of Chachmah and does not believe in them. Therefore, afflictions do not help him. ¹ The Evvil will not be chastised, he attributes everything to chance. Some crops, the chaff is easily removed from them. However, the shell of wheat and barley, when one wants to make grits, he must crush them in a mortar until the shell is removed. An Evvil, even if he is crushed in a mortar, the shell will not leave him. It is mixed with his interior. The root of Iveles is in his intellect, unlike a Kesil, whose root is in his power of desire. If you will crush an Evvil, he will doubt the crushing and its purpose. Even though they crush him amidst the grits, that he sees that all their shells are removed, and that this is the purpose to crush, and he recognizes the pestle used to crush, and recognizes that it is made for this, even so he will be unsure and remain in his folly. Even though he sees that encompassing afflictions came, and many Resha'im repented, he will remain in his doubts and Iveles.