It is not even slightly lost on Oliver that this seems like the signature of a manifested, full-dimensional world whose structure is based on some simpler world that had the form of a computer game programmed in a way where it used simple data structures to track things rather than a physics engine.  Several things have been pointing in this direction but this one is pretty strong.

Can Oliver, perhaps by giving way to his own instincts, store the watering can in the backpack and take it out again very quickly and without spilling anything?  And is it then full of water?

It is not even slightly lost on Oliver that this seems like the signature of a manifested, full-dimensional world whose structure is based on some simpler world that had the form of a computer game programmed in a way where it used simple data structures to track things rather than a physics engine.  Several things have been pointing in this direction but this one is pretty strong.

Can Oliver, perhaps by giving way to his own instincts, store the watering can in the backpack and take it out again very quickly and without spilling anything?  And is it then still partially full of water?