Because the particles of water can be separated by the fish.
Why can a needle be passed through cloth?
Because the fibres of the cloth can be separated by the needle.
Why can a nail be driven through a board?
Because the fibres of wood can be separated by the nail.
What name given to this property in these substances?
This property is called Penetrability.
What is necessary in order to penetrate a substance?
We must use a substance harder than the one which we wish to penetrate.
Why will iron penetrate wood?