Earlier quoted context omitted.
In English (en-gb) colloquialism "I ran over the cat" would be perfectly fine as "the cat" is understood to mean "our/my cat". "Your dinner's in the dog", "I locked the keys in the car", et cetera . Similarly in a sentence like "Why don't you and the family come up to the house sometime for tea.". "The house" substitutes for "our house". Now all you need to work out is whether tea is afternoon tea, a cup of tea, or a…
Sure, but presume neither the speaker nor the recipient owns a cat. Without an obvious context ("the cat"? what cats could we both know of?), it's not entirely clear. Saying "the" instead of "a" generally assumes a context that has either been established before during the conversation or outside of it. Imagine a stranger telling you they "accidentally killed the koala". You'd be confused. Not that strangers telling…
Like you say "the item" means there should be an antecedent [previous mention].
If someone said they'd "killed the koala" I'd assume it was a euphemism for something!!