“Your body’s full of veins, isn’t it? Well, you’ve got to fill them up with something, haven’t you?” That’s the mystery of blood, as explained by British comedian Tony Hancock in one of the UK’s best-known comedy episodes, The Blood Donor. But he can’t bear to look at the stuff, still less at the needle that siphons off his precious pint of “AB negative, rhesus positive,” swooning away as the tip touches his arm.