The implant. How did he forget about that? He's used to surveillance -- it would have been a problem in Chaldea if all of the Servants housed there went around unmonitored. He's not, however, used to it being malicious.

"Where I'm from, magecraft was used to communicate over long distances. Didn't need an implant. Guess they only want us to be where they can keep an eye on us. What a pain."