Watching Netflix's "Night on Earth", I discovered that Hippos, or at least some Hippos, have quite a weird appearance in infrared. They seem to be covered by IR bright spots all over their body, possibly excluding their heads.
Something similar can be seen in this video on YT starting around 0:12. The following picture is a screenshot from that video:
What's the reason for this weird pattern? Why are some spots on a hippo's skin warmer than the rest?
EDIT in response to a comment by @jamesfq:
As far as I can tell, these images were taken without the use of IR illumination. The crew in the video linked above were apparently using a repurposed military thermal imager by Selex. As far as I know, these operate without any additional illumination.
@Harun suggested that this might be related to hippo sweat, which looks a bit like blood. But the images I could find (the one below is from here) do not seem to suggest that it forms spots comparable to those in the IR image. But maybe the secretion spreads around the glands it comes from and looks quite different in the IR. It also looks like they sweat on the head, which has a much more uniform appearance in the IR than the body. Of course these are all just single images, maybe not representative.