Ejecting mass is an ability, which can be used to send mass to cells. On the browser version of the game, "W" is the default key to eject mass.
Ejecting causes all of the players cells (that are large enough) to launch a small pellet of mass towards the cursor, similar to splitting. The ejected mass and can be eaten by any cell which is large enough. Cells lose 18 mass per ejection; however, the mass of the ejected piece is only ~72%, only 13 mass is gained upon consumption.
To be able to eject, a cell needs to have at least 35 mass.
Ejecting can be used to transfer food between the cells of a player or to donate mass to allies. It can also be used to create more viruses. As shown in the picture, ejected mass has an angle of spread, meaning that Viruses created may veer off course by ~20 degrees. This spread can be lessened by getting closer to the Virus, although this may also increase the risk of accidentally consuming it.
A good but tough strategy is to eject mass into a virus until it splits, then move to the new virus and split it, so you will have a triangle of three viruses, which you can squeeze in between them to hide inside the virus fort. Big players will be too afraid to try to eat you, because they might hit a virus and split into multiple pieces, which if you are big enough, you can consume the small pieces of the cell.
If ejected mass is left alone long enough, it may function as a spawn point for a new player. They will be the same colour as the ejected mass.
Players should keep in mind that any cell can consume the ejected mass, so it is important make sure that the target cell is close to the ejecting cell.
Ejecting can be used to speed up a player's cell as a less loss-heavy tactic than splitting.
Shooting Viruses
If you eject mass into a virus, the virus will consume the mass and get slightly bigger. If you eject 7 pellets into a virus, a new virus will be shot out in the direction of the last ejected pellet which was fed to the virus, and the original virus will shrink back to 100 mass.
Teaming and Communication with Ejecting
Most of the players in Agar.io know that if they give some mass, they either want to have a team, or bait smaller cells to come closer and then split kill them. This doesn't only happen in Party, but also in other game modes.
Ejecting mass can be used strategically in team mode to slow down other cells, help an allied cell engulf an enemy, or to prevent an allied cell from being eaten. It can also be used to communicate with teammates, such as telling them to split on an enemy cell, then feeding/pushing the piece to eat the cell.