That sounds like the Box2D bug. Crushing actors has a tendency to crash the game - I know it's been worked on but I don't recall the exact current situation (fixed or not).
Turn the collision box into a sensor. It's that easy.
No, its not. Then something isn't going to register solid collisions like it should.
You die when you touch the saw blades. They will be impassable even without collision.
While this works with sawblades, there is also the problem of regular blocks. In level 2, there were moving platforms. However, it pushed into a tile. So, it was possible to be completely crushed between the moving platform and the tile, causing the same bug. Therefore, because I didn't know how/if it was possible to solve this, I decided to make it impossible for it to happen; I didn't catch this one, however.
Anyways, if anyone has a way to fix it, I'd gladly like to hear it!