In the scene where Asterion has a seizure, interesting things are said:
You breathe in again, imprinting that smell, enjoying every second while it lasts. And the minotaur does the same. He buries his nose in your shirt, and a wealth of scents assault him-- the Mediterranean's saltwater, saffron-giving crocus, the decaying petals of deflowered poppies. The smell of bitter, burnt oil that sticks to one's mouth, and the coppery taste leaking from beneath his tongue.
Smell of oil and coppery taste, huh? Suspiciously like ichor and blood, don't you think? Also, this is when Asterion's neck acts up again-- probably the parting wound of his beheading or something. Now, as far as the Master knows, Asterion is fully healed prior to this point. But what if he's not, and that lingering 'wound' has been exuding his blood (in vapor form, at the least) all this time?
But of course, this may be way off and just looking too deep into things. I haven't been able to remember instances of the where the smell of ichor is described. Seeing as it's a divine substance, who's to say that it should smell how it looks like? Next, about the (mortal) blood. How the hell can you make an observation of coppery taste through smell? Besides that, what gave me pause was the location of the taste. 'Beneath the tongue' makes me think about the gold coin Laomedon gave Asterion for Charon's fare. If he was beheaded, the taste should be emanating all over the mouth or at the back of the throat, and not specifically under the tongue. Does anyone know if gold can produce a similar smell?