How does SSH know which key to use?
Solution 1:
I also found the -v option while connecting and it shows what it's doing. Turns out, it tries a bunch of keys that it finds in the .ssh dir. Basically tries whatever's in there.
Solution 2:
There is an option called "IdentityFile"...
I suggest reading a little bit about ssh.config. It is worth it. You can configure the key, port, user name...