The full answer
The throat contains four principal passageways: the trachea, esophagus and two major blood vessels.
The Zabiha standard followed by Shariah Board requires at least three of the four to be properly severed.
If the required passages are not cut, the slaughter does not satisfy the Zabiha requirements.
Answers in the Halal Knowledge Center reflect the standards followed by Halal Monitoring Services (HMS), which operates as part of the Shariah Board of America. HMS certifies only what it checks.