Airplane to Mexico

Tonight while tending to the garden with L (doesn't that so cool!), we were having some fun conversations. One of them went like this:

L: "Mom if I were an airplane, you could ride me all over"
Mom: "Where would we go?"
L: "We could go to Mexico [somewhere she has never been]"
Mom: "Sounds fun - let's go! What would we do there?"
L: "Drink Beer"
Mom: (acting quite stunned - we are not beer drinkers on a regular basis) "Oh yea - why would we do that?"
L: answering quite seriously "Because you can't drink the water in the Mexico!!"

Now where did she come up with that???