2. Good question, I think beams will get stronger as the game progresses to account for the thief gaining weight through the levels. They have a random weight tolerance to introduce some randomness into each playthrough, but I am not sure how well this works out in practice.
3. There is a guard patrolling the upper walkway in the wine cellar, directly below the second room's floor. I suspect he hears the guard being swallowed through the floor and by the time he reaches the spot to investigate, you're gone into hiding. See if you can spot the guard's "I heard a noise" exclamation through the floor as you swallow the guard in the second room? You can also use Z to check where he is, and see when he gets triggered to investigate.
4.1 The swallow attack's collision check originates from the camera, not the player character. I see how this can cause around-the-corner swallows, and will see if I can implement an extra collision check from thief to guard.
Thank you again for the feedback!