Adam Rutherford meets a new creature created by American scientists - the spider-goat. It is part goat, part spider, and its milk can be used to create artificial spiders web. 　　It is part of a new field of research, synthetic biology, with a radical aim: to break down nature into spare parts so that we can rebuild it however we please. 　　This technology is already being used to make bio-diesel to power cars. Other researchers are looking at how we might, one day, control human emotions by sending biological machines into our brains