Mishnah 6 in chapter 8 of Maseches Shabbos continues to deal with the minimum measures for carrying out on Shabbos: the smallest quantity of each material that is considered significant and makes one who carries it from one domain to another liable.
The measures listed in the Mishnah:
"Etzem, kedei la'asos tarvad" - the measure for a bone is a piece large enough to make a spoon from it. Rabbi Yehudah disagrees and rules more leniently: "kedei la'asos mimenu chaf" - even if it is only large enough to make the tooth used in a lock or a key, that is enough to render one liable.
"Zechuchis, kedei ligror bo rosh hakirkar" - the measure for a shard of glass is a piece large enough to scrape the tip of the kirkar with it. The kirkar is the shuttle, which was commonly used in weaving to pass the threads across the loom, and from time to time its tip needed to be scraped. The amount sufficient for such scraping is the measure for carrying out.
"Tzeror, kedei lizrok ba'of" - a stone or pebble: its measure is a size large enough to throw at a bird and chase it away. For example, birds that eat the seeds of a crop, at which one throws something to make them move off.
"Rabbi Eliezer bar Yaakov omer: kedei lizrok bivheimah":
Rabbi Eliezer bar Yaakov disagrees with the first Tanna and sets a larger measure. A stone fit for throwing at a bird is much smaller than the stone needed for throwing at an animal, and in his opinion such a small measure has no significance. What is required is a stone large enough to throw at an animal, a large creature, and drive it from its place.
The reason for his position: a bird takes fright and flees even without anything being thrown at it, and therefore a stone of that size is not a sufficient measure. An animal, by contrast, does not move from its place unless something is thrown at it, and therefore specifically a stone fit for throwing at an animal is considered significant with regard to carrying out.
In summary: this Mishnah lists three measures for carrying out - a bone large enough to make a spoon (and according to Rabbi Yehudah, large enough to make a lock tooth), glass large enough to scrape the tip of the shuttle, and a pebble large enough to throw at a bird - and we learned the dissenting view of Rabbi Eliezer bar Yaakov, who requires for a pebble a measure fit for throwing at an animal.