Continuity mistake: When Walt is practicing his pistol draw in his apartment, he drags over a chair in which to sit during his practice. When he is dragging it, he aligns it directly against the carpet. However, a few seconds later, another shot shows that the chair is now inches away from the carpet, despite him never adjusting the chair.
Continuity mistake: When Andrea drives off we can see 3 bikes parked up by Jesse's house and a car either side of the bikes. When Jesse turns to walk in one car has disappeared. (00:28:35)
Chosen answer: It is part of the ritual for la Santa Muerte. It is a sign of humility and sacrifice.
djm