String.

Get one hundred balls of string and put them in a drawer.

Wait nine months.

Carefully select just one ball.

Unravel it, and tie the ends to each other

Squeeze it all back together,

Run over it with a car,

Rub it in some grass, dirt and paint.

Throw it off some tall things, and retrieve it.

Then put it in the washing machine,

Fling some rubber bands around it to keep its shape,

Then cut a little hole in a wall.

shove it in there,

And plaster over it and paint the plaster the same colour as the rest of the wall.

Wait 17 years,

Then pull it out and place it back in the drawer with the other ninety nine balls of string.