Ice cubes don't kill people. People with ice cubes kill people - well in this case they knock penguins back into the water.
This game is only for fun. Please don't build your own ice cube weapon and then go on an expedition to the North Pole to shoot penguins. First of all, there are no penguins at the North Pole and what with how greenhouse gases are now because of burning oil based fuels you don't want to make a wasted trip.
More importantly, you should not hurt penguins because they have a hard enough time as it is having to waddle to casual gatherings dressed in formal attire all the time. Don't add insult to injury by shooting at them while they are on the way.
Puffins on the other hand - they're open season!