What is meant by the "four veins" (al-awdaaj al-arba‘a)?

Answer

In the name of Allah, know, my son, that in an animal whose meat is lawful to eat, there are the trachea and the esophagus — one for breathing and the other for food — and two blood vessels, one on the right side and the other on the left. All four must be cut for the slaughter to be valid. Allah knows best.