This is the first stage where you can push an enemy into water. However, the water has no current, and there's no new solutions opened up by pushing the snakey in. This is because you can't push snakey in without dying until you use the bridge item (to push the snakey in, you need one of those blocks in front of the bottom medusa), and because there's no current, pushing the snakey in the water is redundant with the bridge item.
3-1 solution
3-2
In testing this stage, I learned that you can't have two eggs in the water at once! This stage also introduces you to the current, but if you mess it up, it's not necessary. You can just push the snakey into the water to your right or below you.
3-3
3-3 solution
You get enough shots to kill both guys, but it's also pretty easy just to place them somewhere that you don't get trapped. I'm pretty sure they never wake up, too. These guys follow you pretty well, so it seems like it'd be pretty hard to trap these guys using the pushable blocks.
3-4
3-4 solution
Just like in 3-3, You've got two enemies, and if you handle the blocks wrong, it's easy to cut yourself off from the solution. However, the tone of gameplay is different, lending itself more to careful planning--you can completely block yourself off from any danger before the enemies wake up (I made use of this stage's pushable blocks!), and you don't get any shots, so messing this up can carry hefty consequences.
3-5
3-5 solution
At first glance, 3-5 looks daunting, but its solution is trivial.
Look at it--the only way to screw this up is if you accidentally push the block too far. I have no idea what the sand is supposed to do. I also don't see any way of clearing this that doesn't take a planned route (that is, in order to clear this, you have to decide what you're going to do before you pick up the last heart). Note that you get zero shots in this stage.
The three-block puzzle skips a floor and doesn't appear in any of these stages.
