On the vaporous surface of freshly brewed tea grows often a thin layer of scum. You will observe on the attached video that not only this layer appears to be crazed, but also that the mosaic formed by these cracks regenerates around every second in a new different mosaic, like a mosaic slideshow. This phenomenon may also be observed on very hot coffee. It looks like a chaotic phenomenon. The attached experience was made in a bowl with very hot plain water and green tea. The cracks suddenly propagate across the scum layer and produce a new mosaic. How to explain such a difference between the patterns ? What make the crack propagate ?

I keep two PET bottles filled with tap water. As I don't intend to use the water unboiled anyway, I hardly ever refill them. Mostly I use them as weights for some fitness training (like dumbells). But once when the water was turned off I actually used water from one of the bottles and refilled it afterwards. Now in comparison with this newly-filled bottle I see that the old one has lost some water. No air has come in instead of it, but the bottle has become a bit floppy. I understand that water molecules are smaller than most molecules in the air, so it is understandable there might be pores through which it can evaporate and nothing comes in to replace it. But are these pores in the bottle or lid itself or does the vapour go through between bottle and lid?

My friend and I work in a molecular biology lab, with regular access to a -80C lab freezer.  The other researchers' and students' sample tubes/vials are kept in boxes or sealed ziplock bags in the freezer.  Occasionally, after a period of storage, a random ziplock bag will be inflated almost to bursting point.  On speculating why this could be, I suggested that the water droplets in the air that is trapped in the bag will freeze rapidly and hence expand, and the pressure increase causes the bag to inflate.  My friend disagrees, reasoning that expansion of water droplets alone can't possibly account for the huge increase in volume inside the bag.  Who is right or, if neither, what is the correct explanation?