What would cause foam to come out of a dead persons nose or mouth?

Foam coming out of a dead person's nose or mouth is often associated with pulmonary edema. Fluid buildup in the lungs. This can occur for various reasons, such as heart failure, severe infection(like Covid pneumonia), or drug overdose. When fluid accumulates in the lungs, it can be difficult for a person to breathe, and they may experience gasping or labored breathing. As a result, air and fluid may be expelled from the lungs, causing a frothy or foam-like substance to appear at the nose or mouth.