Merlin sat hunched over on his bed reading his magic book with index finger of one hand following the text. He frowned for a moment and thought hard. Then a smiled crossed his face. "If I just change this for this…" he muttered.
He heard the door opening and he called out "Hey Gaius! I think I have worked out spell where I can enchant Arthur's armor to make in impenetrable to all weapons!"
When Gaius said nothing, Merlin looked up to see Arthur staring at him with wide eyes.
Merlin stared back and swallowed hard. "Um, You're not Gaius".
A/N
Because we have all done this before, and it's embarrassing.