This is what you need: Paper, drikning straw and water-based drawing ink in different colours.
I don't know in how many colours they come but I have green, blue, black, red and yellow.
Put a small amount of ink on the paper, less is more..
Start blowing the dot of ink around with the straw but don't put saliva in the ink:)
If you make circular motions with the straw while blowing, you get a tree/vein effect. Pretty neat.
Add more colours in and when you are happy with your picture you are done!