I was reminded today of the famous Pavolv's dogs experiment I studied as a freshman in college. (Warning: brief, non-scientific summary of something scientific)
Pavlov fed dogs everyday for a little while. Then he started ringing a bell before he fed them for another while. Then he would just ring the bell and watch them salivate, waiting and expecting food.
I've been in middle school and high school ministry for 6 years. I just ate a slice of pizza here in the office, and got really anxious for youth ministry.