I was playing in an M10 draft awhile back against a pretty good player. Earlier in the game I had casted an Unsummon on his Beserkers of Blood Ridge in response to an Oakenform targeting it.

After that, I had casted an Ant Queen on six lands (three Forests, three Islands), and the turn after that I cast an Air Elemental. However, when I was tapping the mana, I tapped two Islands, then was about to tap the third one but then I mumbled "no.." and then proceeded to tap all of my Forests, leaving only an Island untapped.

I did this because in an earlier game he had cast Earthquake. If he cast Earthquake on me this game, I would have been screwed as I was holding two lands in my hand.

Turns out he actually did have Earthquake in his hand the whole time but was afraid that I had another Unsummon in my hand so he didn't cast it. That won me the game