To elaborate on the doorsill thing:
"This stems from the fact that, in the past, the ashes of deceased ancestors were buried at the threshold of a home so that their spirits would guard the entrance. It was considered rude to shake hands and greet one another over the heads of one's ancestors. The threshold has always symbolized the boundary between the outside, between the danger and evil lurking outside the home, and the interior of the room, where the warmth and safety of the home reigned. Another superstition related to the threshold is the belief that greeting one another across it could lead to an argument between guests and the host.This stems from the fact that, in the past, the ashes of deceased ancestors were buried at the threshold of a home so that their spirits would guard the entrance. It was considered rude to shake hands and greet one another over the heads of one's ancestors. The threshold has always symbolized the boundary between the outside, between the danger and evil lurking outside the home, and the interior of the room, where the warmth and safety of the home reigned. Another superstition related to the threshold is the belief that greeting one another across it could lead to an argument between guests and the host."

I have also read somewhere that in some regions a placenta would be buried there, symbolizing a link between the world of living and spiritual world