Artificial hearts, for example, can cause clots to form when blood hits their surface the girdle material and these clots can cause strokes and death.

Living here means that one mixes freely with anyone who happens to call themselves 'Arab' and the massive differences in currency mean that places that would ordinarily be inaccessible to anyone other than the privileged classes, hold their doors open.

But if large numbers of a host say, birds encounter a great number of people, eventually the virus will find a way to prosper in a new type of cell.