I just found this really cool thing on the Internet. Few of my friends were talking about it few months ago. Ferro fluid is this oily fluid that magnetizes when it senses a magnetic field. When it detects a magnetic field, it solidifies into a spiky blub of...thing. I don't know very much about it, but it's really cool. Check these videos.
How to make ferro fluid:
http://www.youtube.com/watch?v=vsQh1AT6qUE
What happens when a magnet is dropped into it:
Sorry, I couldn't post the first video because there was no embed link.
