What happens if an animal moves or eats my golf ball?

No penalty — you simply replace the ball where it was (or estimate the spot if you're not sure). An animal counts as an outside influence under Rule 9.6, so the ball goes back and you play on.

What Rule 9.6 says

If it's known or virtually certain that an outside influence — and that includes any animal — lifted or moved your ball at rest, there's no penalty. You must replace the ball on its original spot; if you don't know the exact spot, you estimate it using your reasonable judgment. This applies even if the ball hasn't been found yet. If it's not known or virtually certain that an animal moved it and the ball is lost, then you have to take stroke-and-distance relief under Rule 18.2 — back to where you last played from, adding one penalty stroke.

When the spot is unknown

Sometimes you see the animal run off with the ball but you didn't see exactly where it was sitting. Rule 9.6/2 says you use your reasonable judgment to decide where the ball had come to rest before the animal got to it. That's not a guess — it's your best estimate based on all the information you have: where you hit it, the lie, the slope, what your playing partners saw.

If you already played the ball

Say you didn't know the ball had been moved, you played it from the new spot, and only later someone tells you a fox picked it up and dropped it there. Under Interpretation 9.6/3, you didn't play from a wrong place because you didn't know at the time. No penalty for that stroke. But you still have to correct the mistake: replace the ball on the original spot (estimated) and continue from there.

Exceptions that change the answer

• Wind moves an outside influence that then moves your ball → Wind itself isn't an outside influence, but if wind blows a plastic bag, a towel, or something else that then moves your ball, Rule 9.6 still applies — the object is the outside influence. You can either replace the ball or take relief under Rule 15.2a from the movable obstruction.
• Your ball was moved from out of bounds by an animal and you played it → If the ball had come to rest out of bounds, an animal moved it onto the course, and you played it not knowing — you played a wrong ball. No penalty for the wrong ball under Rule 6.3c(1), but you must correct the mistake under Rule 18.2b (stroke-and-distance for a ball lost or out of bounds).
• It's not known or virtually certain an animal moved the ball → You play the ball as it lies. If the ball is lost and you can't say an animal took it, it's stroke-and-distance under Rule 18.2.

Frequently asked questions

A bird picked up my ball and flew off with it — what do I do?

That's an outside influence. No penalty. Estimate where the ball was at rest before the bird grabbed it, place a ball there (or drop if the original spot is in the general area and you're taking relief), and play on.

My ball is gone and I think a dog ate it, but nobody saw it happen.

If it's not known or virtually certain the dog took it, the ball is simply lost. You go back to where you last played from under stroke-and-distance (Rule 18.2) with a one-stroke penalty.

Do I have to find the ball to replace it?

No. Rule 9.6 applies whether or not the ball has been found. You replace a ball on the estimated original spot — you can use a new ball if the original isn't recoverable.

What if I play the ball after an animal moved it, not knowing it moved?

No penalty for playing from the wrong place because you didn't know. But once you learn it was moved, you must replace it on the original spot (estimated) and continue from there.

Is a worm or insect an outside influence?

Yes — any animal is an outside influence. If a worm casts move your ball on the green, that's Rule 9.6. Replace it, no penalty.