Learn English – What phrase can describe the final moments before a deadline

As FumbleFingers pointed out in his comment, it's from Shakespeare's King Henry V (Google sample). Seeing it in the context of the script (with its original punctuation) makes it easier to understand. The man sold the lion's skin while the lion was alive, but was killed by hunting the lion. The meaning behind it seems to be that the man sold something he did not have (the lion's skin) and failed to get it (died). Not only did he fail to deliver, he was ruined by his folly.

This could be used in two different ways in the novel (I'm not familiar with it, so I can't say which it is):

• The banker swindled the men (akin to selling a lion skin he does not have) and will be punished for it (killed in the hunt)
• The four men are depending on their money that they have not yet gotten back from the banker, and pursuing it will be their downfall.

I think your Person 2 is supposed to say that the subject of the verb "involve" is "adverse reactions." I agree with the example that tchrist says, although the "Person 2" example wouldn't make sense. I think you should edit your question title to ask for the subject of the verb, because the subject of the sentence is obviously "food allergies."

And scientifically, that would make the most sense to me. It's not usually the food that's the cause of the problem, but the body's improper immune response to it. The body is normally able to discriminate between food (which should have no immune response) and bacteria, fungi, and other bad things (which should be attacked by your mucosal immune system). But you were asking about grammar, not biology...

I put this in a comment but also want to add it here. The next sentence from the original FAO report says: "True food allergies may involve several types of immunological responses." I think that makes it unlikely that the scientists intended to use the definition in the third example.