There are rocks all around the level that the monster can pick up in his mouth and spit out at the monsters. The monsters are stunned when they are hit with the rock. While the monster is stunned you can eat it.
To clear a level you need to eat all the monsters in that level. As the levels progress there are more and more monsters. The challenge in the later levels is to eat the monsters before they wake up and before other monsters come and eat you.
There is also food items spread around the level. If you eat the food items they will give you extra points. Once you die and the game is over, you can submit your score.
I found Square meal cute and entertaining. There is enough challenge in the later levels to keep you coming back for more.