If it is their wands that cannot interact, that means that they can use wandless magic on one another. I don’t remember if it was ever stated in the story that Quirrell cannot do wandless magic on Harry, but if he can that gives him a very big advantage when it finally comes down to a showdown between them.
I had neglected that. Now I wonder whether it is their magic that can’t interact, or their wands.
If it is their wands that cannot interact, that means that they can use wandless magic on one another. I don’t remember if it was ever stated in the story that Quirrell cannot do wandless magic on Harry, but if he can that gives him a very big advantage when it finally comes down to a showdown between them.
When their whatever interacted, to save himself Quirrel threw away his wand, and it seemed to help.
If it’s similar to in canon, their wands are brothers but Harry touching Quirrel will also cause problems.