Sacrificing a permanent means moving it from the battlefield to its owner's graveyard as a cost or effect (CR 701.17a). The moment you sacrifice a creature, it leaves the battlefield and no longer exists as a game object. There is nothing left to sacrifice a second time.
Even if two sacrifice outlets are both available simultaneously — say, two separate activated abilities whose costs each say 'sacrifice a creature' — you can only pay that cost with a given creature once. After the first sacrifice, the creature is in the graveyard and is no longer a legal target or legal cost-payment object for any other ability (CR 701.17b).
It's worth noting that if you activate two sac-outlet abilities at the same time (placing both on the stack), you still need a separate creature for each. You cannot declare the same creature as the sacrifice for both; each ability's cost must be paid with a distinct creature (CR 601.2h, 602.2a).
Example: You control Viscera Seer and Carrion Feeder, both of which say 'sacrifice a creature.' You activate both abilities and put them on the stack. You must sacrifice two different creatures to pay both costs — you cannot sacrifice one creature to pay for both, because after it's sacrificed for the first ability it is already in the graveyard.
Unofficial fan resource — not affiliated with or endorsed by Wizards of the Coast. Answers are AI-generated estimates grounded in the Comprehensive Rules and are not a substitute for an official judge. Verify anything match-critical.