When chatting informally, either in person or over text, it seems common to shorten the sentences by omitting pronouns:
- Made it home?
- Yeah. Should've taken a bus.
- Hope you don't catch a cold!
However, in some cases it sounds unnatural, even if the pronoun is heavily implied:
- *Closed the door?
- *Should close it.
Are there any rules as to when one can and cannot shorten their sentences in this way, or does it boil down to some phrases just being more idiomatic than others?