For the life of me I can't understand why I'm stuck at 98% insights, but other than that it's a marvellous experience! Bravo!
Edit: got it! Nice cat sounds btw :D
Any combination of items that sum up to 999. The easiest to remember is: face to the door, turn right and get the first item, then turn around and go to the last item at the end of the left corridor, and take the first 3. So like a statue to the right, and then the collector’s edition iirc, and the two closest to it.