Shevuot 17B

אלא אי אמרת דוקא גמירי, היכי משכחת לה?

But if you say that it is learned as a tradition specifically that if an impure person tarries long enough to bow down, he is liable even if he does not exceed the time required to go out the shortest way, then how can you find these circumstances?

אמר אביי: מאי קושיא? משכחת לה כגון שבא בקצרה והפך בצינורא, וכדרב הונא ⁠– דאמר רב הונא: זר שהפך בצינורא, חייב מיתה.

Abaye said: What is the difficulty? You find it in a case such as where he went out from the Temple via the shortest way, but as he was leaving he turned over one of the limbs of an offering on the altar with a fork [betzinnora]. This is an action that takes only a brief moment to perform, and yet it is considered priestly service, in accordance with the opinion of Rav Huna. As Rav Huna says: A non-priest who turns over part of an offering on the altar with a fork is liable to receive the death penalty, because he engaged in Temple service restricted to priests.

גופא ⁠– אמר רב הונא: זר שהפך בצינורא, חייב מיתה. היכי דמי? אי דלא הפך לה לא מיעכלי ⁠– פשיטא! ואי דלא הפך בהו נמי מיעכלי ⁠– מאי קא עביד?

The Talmud proceeds to analyze the matter itself: Rav Huna says: A non-priest who turns over part of an offering on the altar with a fork is liable to receive the death penalty. What are the circumstances of such a case? If in the event that he had not turned it over, the offering would not have been consumed by the fire, then it is obvious that the non-priest is liable, as he performed the service of burning the offering on the altar. And if in the event that he had not turned it over, it would also have been consumed by the fire, then what service did he perform? Even without his action, the offering would have been burned.