The HoverDoc is a curious bug-like object (apparently some sort of life-form) that follows around Creatures it is dropped upon.
It has an accompanying medical device, the Creature Care Kit. The Creature Care Kit appears as a slide out panel when the HoverDoc is locked on to a Creature. It indicates a Creature's drives and most pressing needs (hunger, crowdedness, etc), as well as details of bacterial infection (with the option of a remedial spray), poisons (with recommended treatments) and fertility (with a pregnancy monitor).
Windows Hint: Press CTRL+SHIFT+H in DS to go to the HoverDoc. Be careful, if the hand is holding the HoverDoc, or it is in the inventory, a new HoverDoc will appear!
There is a good overview of the HoverDoc at Alien's Creatures World.
The only two toxins that the Creature Care Kit sees as an 'emergency', allowing you to inject the cure directly into the norn, are cyanide and glycotoxin.
The HoloDoc is also a hand-shaped COB for C1 and C2, if the HoverDoc isn't what you were looking for.