Ravenous Rotbelly

• WWizards of the Coast2021-09-24
  Official Ruling
  After you sacrifice one or more Zombies, a second ability triggers. Players may respond to it before they have to sacrifice creatures.
• WWizards of the Coast2021-09-24
  Official Ruling
  As the reflexive triggered ability resolves, first the next opponent in turn order (or, if it's an opponent's turn, the opponent whose turn it is) chooses the creatures they plan to sacrifice. Then each other opponent in turn order does the same. Finally all chosen creatures are sacrificed at the same time.

Rulings via Scryfall