I'm not sure how many of you have noticed this phenomenon in your snakes...I know I missed it for years, lol. Between being blue and right before they shed, I've got several adult snakes that get edematous at the back of their throats. I'm assuming this is due to congestion from a "too-tight" skin leading to mild backup of lymphatic drainage and hence, edema of the head. At any rate, it scared me the first time I saw it, now it just intrigues me. 
Here's the appearance from a profile, swollen corn on top (notice the swelling under her jaw), and a normal corn on bottom.
Now for an inside the mouth look...
And here's a normal mouth (right) for comparison next to the swollen throat (left):
Here's the appearance from a profile, swollen corn on top (notice the swelling under her jaw), and a normal corn on bottom.


Now for an inside the mouth look...


And here's a normal mouth (right) for comparison next to the swollen throat (left):

