Eric knew full well that Kar'en was an impossible enemy to plan against.
'Even if we create an elaborate plan, we still have to communicate it to one another.'
When it came to 'characters' like the Dragon General, it was possible that she had some special Skill that would allow her to bypass Sound Magic, making it very likely that she would see through whatever strategy they made.
The more complex a plan was, the more important it was to clearly communicate it with allies.
'Even if we speak to each other and use English, there's no guarantee that she won't be able to decipher the plan somehow.' The more Eric thought about it, the more he felt like they were stuck.
… So he found a loophole.