Quote Originally Posted by Thunderous Mojo View Post
Prestidigitation can instantaneously clean or soil an object no larger than 1 cubic foot.

Instantly cleaning an apple isn't going to be helpful if the poison is inside the apple; if, however, the apple was coated externally with contact poison, "cleaning" the apple should likely include removing the application of poison.

Prestidigitation being able to clean the layer of poison applied to the arrowhead, seems a sound use to me.

The only pitfall I see, is the magical cleaning will likely apply to the single drawn arrow. If the Yuan-ti notices that the arrow has been de-venomed, the Yuan-ti may simply draw another envenomed arrow from their quiver.

Now, if the Yuan-ti decides to use their action to Investigate the arrow...that is probably the best outcome. Alas..I don't think this outcome is likely.
The Yuan-Ti already has the arrow ready to fire. If I were playing the Yuan-Ti, I'd fire the arrow, mildly annoyed at losing the poison, then draw another envenomed arrow for the next shot. Seems most logical/reasonable.
Noticing the suddenly-clean arrowhead shouldn't be hard. The tip of the arrow is in the middle of their field of vision as they go to fire.

Saving throw feels applicable, as it is a carried item and you are getting a combat effect from a spell. All of the damaging/controlling spells generally give a saving throw or require a roll to hit.