Pellets (aka agar, rainbow pellets) are little dots that spawn randomly all over the map. They give 1 mass when eaten, but can grow in size over time.

They may spawn randomly on the server, but can also be shot out of mother/spawn cells on Experimental and Battle Royale servers.

Eating pellets is the most common way to gain mass. The other ways include: eating other cells, eating a virus (when large enough to eat them) and eating W mass ejected from other cells.