The theory of running out and placing something else quick back in the same position sound a bit stupid. Cause i rather run super fast away than place another object there.

My theory is that kawarimi is a high level ninjitsu that uses chakura to place an object to the person's position an at the same time the person is "teleported" to a position he likes. It also involves an illusion on the attacker making him "see" the object as the person. However kawarimi cannot be perfromed if the person is held down by something. (e.g. dog biting down, a sword struck on the person and still held by the attacker) I does not involve hand seals cause it is stupid if the attacker is attacking you and sees you performing the "kawarimi handseals", cause he would know that he use using that jitsu and would'nt attack.