I think we do a very poor job of explaining the concept of "substance" in the doctrine of transubstantiation. The concept comes from
Aristotelian ontology about the nature of objects. But that doesn't well translate to medieval society in which even the nobility is rarely literate, much less well-read in the philosophers of antiquity.
So the result is that you get silly things like the
"Miracle of Bolsena", in which the consecrated host supposedly bled.* So people ran around for a thousand years misunderstanding the entire theory, thinking that the host was supposed to actually have Christ's DNA or some $#@!.
From a Aristotelian philosophical view, objects have a certain substance. A lamb has a certain substance from which we know it's a lamb. It is warm to the touch, it goes "baaa," it has a beating heart and breathing lungs. It has a brain that thinks cute little lamb thoughts. But it also has certain attributes that you can see. It has soft wool and a black nose and four legs. But those aren't the substance.
If the lamb dies, its attributes may be the same. Even though it's dead, it still has soft well and a black nose and four legs (and mighty yummy chops). But it no longer has the substance of a lamb. The substance of a lamb has been replaced by the substance of a dead mammal, complete with maggots and smell of decay.
So it is with the consecrated host. After consecration, it has all of the attributes of bread and wine. But in substance, it is something else entirely. It's a real sit down and go "huh" kind of thing. Unfortunately, the Western Church has done a poor job of explaining the mystery of transubstantiation--in many ways I think the Eastern Church gives a much more elegant description.
* That's not to say that the miracle didn't happen. The consecrated host may have bled for all I know. But its bleeding didn't exactly lead to a very good understanding of the doctrine of transubstantiation in the generations to follow.