GarcÚs finding a lottery ticket at the rebel campsite... And Captain Vidal shouting into the wilderness: "You forgot your lottery ticket! This could be your lucky day!" Much later, as Mercedes escapes from the mill, you can actually see GarcÚs standing by the radio and presumably listening for the results of the lottery, before irritably crumpling the ticket into a ball and throwing it away.
In the beginning, there's Ofelia's rather nonchalant statement: "I just saw a fairy!" The fact that she's just so deadpan about it is hilarious.