Birdie vs. Waterfall?

Last night we had our favorite Rileys over for homemade pizza. I wish I had taken pictures, I made a spinoccoli pizza (Spinach/Broccoli with a white sauce) and Chad made a "man pizza" with lots of cheese, bacon, and sausage. I have to say that the Spinoccoli pizza blew the man pizza out of the water. It sure was tasty! However, after the pizza was done and the Graham Canyon ice cream was broken out (BYU creamery win!), we came upon a slight disagreement.

What is it called when you drink water without putting your mouth to the bottle/cup?

My sister and I firmly believe the answer is a "birdie" sip. However, the boys would not relinquish their hold on the term, "waterfall". We decided to bring the matter to facebook and both Rileys posted on their wall a survey to see who was more correct. The stakes are high... whichever team wins (girls or boys), gets to throw 10 snowballs at the losing team. That is, if it does actually snow at some point this week.
The survey will end today at 5:00 p.m. and then we will see who has come out victorious. And so the Birdie vs. Waterfall battle has commenced.