At least in that example the Cat is everything the Animal is.
Some examples go as bad as: Square inherit Rectangle inherit Shape because "all squares are rectangles and all rectangles are shapes"......
Some examples go as bad as: Square inherit Rectangle inherit Shape because "all squares are rectangles and all rectangles are shapes"......
1. Inheritance is IS-A. A Square ISN'T-A Rectangle because it breaks Rectangle's contract. If I give you a Rectangle object, you know that you can change the width without affecting the height. If I give you a Rectangle reference which happens to be a Square instance, setting different width and height will either cause a crash/exception, which is not what a Rectangle should do, or ignore one of the values and set the height equal to the width, which is also not what a Rectangle should do.
2. A bit subtle, maybe, but important. While your renderer probably has a method taking Shape objects, it is very unlikely that you have an interface somewhere that takes Rectangle objects. In that case, what you actually need out of this is some code reuse between Rectangle and Square, not type inheritance.