Liquid water can have another form. One is 20% less dense than the other, but elusive.

 At -63C, liquid some H20 water molecules restructure to a 20% less dense form.  Because no one could observe water at that temperature without it turning to solid ice, this couldn't be proven until high speed recording captured the change before the solid ice could form.  It seems to be a dynamic equilibrium at local levels and the authors wonder if this property of water might appear at body temperatures in minute loci, affecting biological communication.  The geometry behind the density isn't described at the link.