There’s a difference between a spherical cow, an internally homogenous spherical cow, and a rigid, internally homogenous spherical cow. The typical spherical cow is said / written as the first type but is actually assumed to be the third type.
The closer we look, the more these details matter.
Eggs are a particularly fun example that’s readily to hand. The easiest way to tell if an egg is hard boiled is to spin it on your kitchen counter. Taking care not to let it fall off to the floor in case you’ve guessed wrong about it being hard boiled.