Correct me if I'm wrong, but I don't think humans are reptiles, phylogenetically. The Synapsida (containing mammals) and Sauropsida (containing reptiles) are sibling groups inside the Amniota.
They're not infailable, though. For example, TeX's primitive for fractions is actually {a \over b}, LaTeX's \frac is a macro on top of that. The consequence is that while typesetting a formula, the engine does not know the current text size, since an \over further down the line may put the entire thing into a numerator. Dealing with this can be quite a pain when writing math macros.