1. A method of early detection of a heat-related illness, the method comprising: receiving, via a thermal sensor that has a field of view, thermal signals from a group that comprises no fewer than three animal subjects; generating thermal data from the thermal signals; identifying, for each animal subject, a subset of the thermal data that corresponds with at least a portion of the animal subject; comparing the subsets of thermal data to determine whether any of the animal subjects is a thermal outlier relative to the remaining animal subjects; generating an image of the field of view of the thermal sensor; and identifying an animal subject within the image as a thermal outlier.