What are the boundaries of the throat such that if something reaches them a person's fast is broken, even if he is able to return that thing after it has reached them, or is the fast only broken upon swallowing the thing?

The limit of the throat that invalidates the fast by something reaching it is its interior, from which whatever reaches it cannot be expelled. Some scholars have defined the apparent part of the throat as the exit points of the letters Kha (خ) and Ha (ح). Thus, if something reaches these points and is then swallowed, the fast is broken. However, if it does not reach the apparent part and remains within the inner part (the exit points of the Hamza (ء) and Ha (ه)), then the fast is not broken by its return.