Some substances, called suspensions, have very strange properties: they change from solid to liquid simply on being touched.
Even simple substances can behave this way. Cornflour, for example, does not mix with water, but stays as a suspension of flour particles in water. When green colouring is added it makes green slime. Jab it and it will act like a solid, leave it and it will creep about, squeeze it and it will go runny – it's one of the wonders of science.
