That is indeed the kind of slip of tongue that might make Buckingham curious, suspicious. But given that his suspicion has already reached beyond its peak there is little that can be changed by George's comment, although it certainly confirms what the duke already knew beyond a shadow of doubt.

Murder. Murder by this dreadful creature that evokes such ghastly memories of death, murder most vicious and under the pretense of lending her aid, murder--

Murder that lacks subtlety and is doomed to fail.

Lord Buckingham grins.

"You suspect... death won't work on you?"

He extends his hand towards George, towards the mask she offers.