To abuse Greenspun's 10th - Every untyped codebase contains ad-hoc, informally specified, bug-ridden, slow implementation of types (written as unit tests).
edit: as pointed out - I need type checking on my words
edit: as pointed out - I need type checking on my words
Moreover, they're typically able to do more sophisticated checks than most languages (e.g. similar to the kind of sophistication of Haskell's type system).
(yes, I know what is going to be replied... IME, they actually fail in prod vanishingly rarely)