Another clever mindgame springs to mind:
"You'd like to think that, wouldn't you? You've beaten my giant, which means you're exceptionally strong, so you could have put the poison in your own goblet, trusting on your strength to save you, so I can clearly not choose the wine in front of you. But, you've also bested my Spaniard, which means you must have studied, and in studying you must have learned that man is mortal, so you would have put the poison as far from yourself as possible, so I can clearly not choose the wine in front of me!"
'You're trying to trick me into giving away something. It won't work.'
"It has worked! You've given evertying away! I know where the poison is!!"
Of course, thirty seconds later, he was cleverly dead.