How does Zika virus cause birth defects? This study demonstrates that the birth defects associated with Zika virus infection arise due to the detrimental effects of type 1 interferon, which (paradoxically) is produced by your immune system to protect you from viral infections. This is a story that is interesting in its own right, but note the wonderful experimental design in this study: the control fetal mice that produce the type 1 interferon receptor share the same womb as the experimental fetal mice that lack this receptor (paragraph 7). Fetal mice that lacked the receptor had high viral loads, but were relatively healthy. Fetal mice that produced the type 1 interferon receptor were spontaneously aborted and had other developmental abnormalities. In biomedical research, experimental design is everything!