Dean Stretton imagines a case in which an emergency arises and a person is faced with the choice of rescuing ten frozen human embryos or five adult patients. Since virtually everyone would choose to save the adult patients rather than the embryos, this indicates that the patients have a higher moral status than the frozen human embryos. 
On the surface this seems to make sense. After all, the pro-life case is that from fertilization unborn human beings are morally equivalent to adults. You would think the ethical thing to do would be to rescue the greatest amount of humans possible, in this case the ten embryos. But if we would allow embryos to die in the fire by rescuing another human, how does that justify our intentionally killing them through abortion?