One of the customs discussed is the placement of the zeroa on the Seder plate. Instead of using an actual foreleg, which would more closely resemble the Korban Pesach, the minhag is to use the neck of a chicken.

Additionally, most of the meat is removed from the zeroa. The Rebbe explains that this is done in order to create a clear distinction between the zeroa and the actual Korban Pesach. Since the Korban Pesach may only be eaten in the Beis HaMikdash in Yerushalayim, we must avoid any appearance that this is an actual korban.

By removing most of the meat, it becomes obvious that this is only a symbolic remembrance and not something that could be mistaken for a real offering.

The Rebbe further brings, in the notes from Sefer HaSichos, that the use of a chicken neck also serves this purpose. A neck is not considered an important or choice piece of meat, unlike the Korban Pesach, which had to be brought in a dignified and significant manner.

Thus, both elements—the removal of meat and the use of a less significant part—reinforce the same idea: to distance this symbol from the actual Korban Pesach, making it clear that it is only a zecher.

Summary
The zeroa is prepared in a way that avoids any resemblance to the Korban Pesach. By using a chicken neck and removing most of the meat, the minhag ensures it is clearly symbolic, preserving the distinction from the actual korban.