[frubam]

Originally Posted by s_b

Just to clear this part up (I'm assuming you are talking about how Touma knew where the system was so easily)...

Spoiler for but (novel details here):

I guess it might have seemed that way, but that is simply the manga doesn't reveal Touma's thoughts as much. The manga kind of cuts a bit here...

Touma actually touches Index on the forehead first, in order to disable the system, but nothing happens. So he thinks about it, and realizes that it was on a place near the brain but he hasn't touched, and he comes up with the answer (inside her mouth), and then he stuffs his hand in.
It seems the manga cut it so that it seems he immediately realizes it was in her mouth.

The symbol/system is magical, completely.

Thanks for the clarafication on that and the debunking of my magnificient theory, if i do say so myself .