[All he's hearing is not to dilute it into a safer form before trying, if the opportunity arises. Not a problem in the slightest!

As for the berries...]

Oh, I was going to after! I figured if you overheard before we started, [Knowing of any negative effects might pose a risk to cooperation? No, he shouldn't be that honest about it.] our expectations might obscure their strength. I was hoping to see everything firsthand, so that wouldn't do.

This way's more like a blind trial! It's how I develop most of my own medicine, as well.