In the quiet architecture of the developing feline body, viruses do not wander blindly — they seek specific molecular doorways. A new study has charted, for the first time with precision, where those doorways exist across the organs of cat fetuses, revealing that susceptibility to infection is neither uniform nor predetermined, but shaped by tissue, timing, and individual variation. This foundational mapping of viral receptor expression offers science a reference point from which to better understand how disease begins before birth, and why some lives prove more vulnerable than others from the