> Arrays are covariant in their type param, so I can pass a `Dog[]` into a function that accepts `Animal[]`. If that function adds a `Cat` to the passed array, the compiler is perfectly happy, but we'll see a runtime error.

The same is true for Java arrays. I thought the Liskov substitution principle was tautological when I first heard about it, but it seems like the original designers of Java disagree. Another example (albeit from the standart library, not the typesystem itself) is that if you try to modify a `List` or similar collection, it may throw an `UnsupportedOperationException` because it's immutable - instead of having a superinterface with only non-mutating methods and only implementing that.