This is me. My mouth is dark (cool) because of my breath. The black halo is an artifact created by the camera.
Neal Butler sent me this info about the halo:
The technical reason for the dark halo around bright objects is the chopper used in the Raytheon (now L3) system. The chopper is transparent and alternately blurs the image or not before it reaches the focal plane. The digital processing then subtracts the blurred image from the sharp image. In the photography world, this is called "unsharp masking". In the digital signal processing world, it is a spatial high pass filter.
The chopper is really cool. It is a thin plastic film, with very high IR transmission. Portions of the film have a 1/4 wave thick diffraction pattern embossed on them. The diffraction pattern is selected to have no energy in the zero order. That is, it effectively blurs the image. As the chopper rotates, so does the diffraction pattern, so no artifacts from the pattern are visible in the imagery. This is so cool because the chopper weighs and costs almost nothing.
The dark halo around bright objects is just the negative of the blurred bright object. The chopper is necessary because ferro-electric detectors have no response to DC. The chopper modulates the scene radiance at 30 Hz so the detectors respond to it.
Raytheon chose to do things this way because it greatly reduces the dynamic range and complexity of the signal processing. This basic scheme has been around since about 1979, when the group was owned by TI.
Modern micro-bolometer focal planes do not have a chopper and do not show these effects.