Shekalim, Chapter 3, Mishnah 3. The Mishnah continues describing how the Terumah of the Chamber was taken, and in particular the attitude of the members of the household of the Nasi, the Nasi of Israel, toward this Terumah.
The words of the Mishnah:
"shel Beis Rabban Gamliel hayah nichnas" - the members of Rabban Gamliel's household, when they came to donate their half shekel, would walk in together with the man who was about to take the Terumah of the Chamber.
"v'shiklo bein etzbe'osav" - his half shekel was held between his fingers.
"v'zarko lifnei ha'toreim" - and he would toss it right in front of the man who was taking the Terumah.
"v'ha'toreim miskavein v'dochako l'soch ha'kupah" - the one taking the Terumah would deliberately push it into the basket, so that Rabban Gamliel's half shekel would be among the half shekels that were actually taken as Terumah, the ones with which the offerings were purchased.
The distinction of a shekel actually used:
The Terumah of the Chamber was always taken in the name of all of Israel, and every single person had a share in it. Even so, there was a special significance and a special idea in having one's own shekel actually be used to purchase the offerings. Obviously an individual cannot purchase all the offerings - his money is enough only for one portion, for one offering or two - and nevertheless this was something that could be achieved.
The Gemara in Horayos teaches that there is a particular value in a person's coin being the one actually used, since in this way his connection to the offering is greater. However, this holds true only with regard to that specific offering, and it does not extend to the rest of the offerings. Even so, this special arrangement was made for the household of Rabban Gamliel.
"Ein ha'toreim toreim ad she'yomar lahem etrom":
The one taking the Terumah would not perform the actual act of taking until he said to those standing before him - people who stood outside the Chamber or right there in front of him: "Etrom?" - meaning, shall I take the Terumah? "v'hein omrim lo: t'rom, t'rom, t'rom" - and they answer him three times: take the Terumah.
The language of the Sages in threes:
This is the way of the language of the Sages, to say things three times. The same idea appears in the harvesting of the Omer for its offering, which was done in the same manner: they would say "this sickle, this sickle," saying it three times. This is how the procedures for the offerings were carried out.
In summary: In this Mishnah we learned about the practice of the household of Rabban Gamliel, who would toss his shekel in front of the one taking the Terumah, and that man would deliberately push it into the basket - because of the special distinction of a shekel that is actually used to purchase the offerings, as explained in the Gemara in Horayos. We also learned the order of the announcement: "Etrom?", and the response of those standing there, "T'rom, t'rom, t'rom," three times, in keeping with the way of the language of the Sages in the procedures of the offerings.