איוב, פרק מ״א, פסוק ט״ז

The inner nature of this fearsome creature is defined by absolute stability and an unshakeable core, standing in stark contrast to the biology of all other animals. Its heart is exceptionally strong, solid, and firmly established [רש״י, רמב״ן, אבן עזרא]. It is formed as if cast from a hard, unyielding material [רמב״ן, אבן עזרא]. While the hearts of typical living things are hollow, constantly beating, and shifting within the chest, this creature possesses a heart that is a single, heavy block entirely devoid of empty spaces. It remains fixed in its place like an immovable foundation stone [מצודת דוד, מלבי״ם, תקות אנוש]. Functioning as the anchor of the creature's body, it rests at the center like the hub of a wheel or a king securely ruling his country [תקות אנוש].

This physical density and stillness directly shape the creature's temperament. Because its heart is entirely solid and immovable, it is completely incapable of experiencing fear or nervous excitement [ביאור שטיינזלץ].

To further illustrate this unyielding nature, the heart is compared to a heavy millstone. Millstones are typically formed by splitting a single large rock into two matching pieces [מצודת ציון]. Yet, the comparison focuses specifically on the lower millstone rather than the upper one [רש״י, מלבי ם באור המילות, ביאור שטיינזלץ]. This distinction highlights several key traits. First, while the upper stone constantly turns and rolls to grind grain, the lower stone remains permanently fixed and never moves [רש״י, מלבי״ם, ביאור שטיינזלץ]. Second, the lower stone is a completely solid block, lacking the central hole found in the upper stone where grain is poured [מצודת דוד]. Finally, the lower stone, particularly at its center, is the stronger and firmer of the two [רלב״ג, רמב״ן, אבן עזרא].

Beyond physical biology, the imagery of the lower millstone captures the creature's incredible endurance in the face of hardship. Just as the heavy upper stone constantly grinds and presses down upon the lower one, severe troubles may bear down on the creature. Yet, despite the immense pressure, it remains entirely stable and completely unshaken [אלשיך].