Merlin and Gaius in “The Dragon's Call”

Hello? Gaius? (He spots Gaius standing and clears his throat. Gaius is startled and falls.)

Whoa!

What did you just do?

Ehm.

Tell me.

I ... I ... I have no idea what just happened.

If anyone has seen that ...

Oh no, that was .. that was nothing to do with me, that was.

I know what it was. I just want to know where you learned how to do it.

No I..

So how is it that you know magic.

I don't.