Each time you solve one of the puzzles in the bomb-room, see if it's made any changes to the room before.
Pardon me for being a bit of a thicko. But the only thing that seems to change is the cat giving me a hint, which is admittedly something I never noticed before. I can't figure out if there's a way to get back through the laser.
Look closer. In the 2nd or 3rd challenge to deactivate the bomb, it also opens a hidden corridor. It closes as soon as you get that challenge though.