I have had my doubts too but my recent experiences make me think that what you get out are really gallstones...
this is because late 2005-2006 I got a lot of stones in my first 4 flushes ...green peas...after that fewer and fewer and now (today) I pooped out a large turd (ICK!) that floated and was the same color of olive oil! Actually.. the last three flushes i don't get anything green at all. so i think I am done!
If the Olive oil and gallbladder bile combined to make something that looks like gall stones you'd think we'd get the same result everytime!