Because English does not have a case system. In languages like Russian, German etc. words have different endings based on their position in a sentence. So, it's clear what you meant because lady would be in the objective case and dog in the nominative. In English, however, the word lady and the word dog will look the same no matter its place: our only cases are possessive and plural, and pronouns have distinctive subjective and objective cases, and nouns have plural forms (unlike in Japanese,) but these cases are not nearly as extreme as in other languages. This is why word order is very, very strict in English.