Recall that artificial objects which interfere with play are obstructions. Natural objects that interfere are called loose impediments. Since golf is meant to be played in Nature as we find it, the rules for loose impediments are much different than for obstructions.
Loose impediments include stones, leaves, twigs, branches, and such. Goose poop is a loose impediment, as is any other animal waste matter. (The Rule book more politely calls it dung.) Worm casts are loose impediments. I’m not sure what that is. Maybe it’s because we don’t have them where I live. We do have goose . . ., oh, never mind.
There is a however regarding loose impediments. A big however. A loose impediment cannot be something fixed or growing (a weed), solidly embedded, or adhering to the ball (mud, goose poop). Then it wouldn’t be loose, would it? I played with a guy who hit his ball next to the green and it came to rest a few inches away from a thick-stemmed thistle. The thistle was in the way of his backswing. He proceeded to stomp the thistle and beat it into oblivion with his sand wedge, which he then used to chip on onto the green and sink the putt for his par. Or so he called it.
Loose impediments may be removed without penalty, except if the impediment and the ball are both in the same hazard. When your ball is near a pine cone, you may remove the pine cone, but if they are both in a bunker, the pine cone stays put.
If you cause the ball to move when removing a loose impediment, except when the ball is on the putting green, there is a one-stroke penalty and you must replace the ball. For example, your ball is lying against a twig. If you think the ball might move when you remove the twig, leave the twig alone.
When the ball is in motion, a loose impediment that might influence the movement of the ball may not be removed. Camilo Villegas was disqualified from a tournament in 2011 when he chipped up a hill. The ball rolled back down, and Villegas swatted away a loose divot lying in the hill in the way of the ball. The penalty would be two strokes, but because he signed his scorecard without taking the penalty, he got the DQ.
All this is Rule 23.
Loose impediments can be tricky. Loose sand and soil are loose impediments on the putting green, but nowhere else. Rory McIlroy got caught earlier this year brushing away loose sand that was in the way of his shot, but not on the putting green. Two strokes, courtesy of his playing partner, Luke Donald.
Loose impediments can also be quite funny. Here, from the Decisions, are examples of loose impediments: half-eaten pear (though no pear tree is in sight), banana peel, ant hill, dead land crab, snake (but only a dead one. A live snake is an outside agency.), a fallen tree, but only if it is detached from its stump.
An insect on your ball is a loose impediment and may be removed, but be careful not to move the ball if it does not lie on the putting green. If the ball is in a bunker, the insect may be removed only as long as it (the insect) is not touched.
If you are about to take a drop, you may remove loose impediments before you drop the ball.
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