As a participant observer she made frequent purchases from Coke machines. To all outward appearances, she did what others did, but she approached each vending machine with an additional purpose: to watch her own actions, the behavior of others, and everything she could see in this social situation. When she had to wait her turn, she focused on how people interacted with the machine, the steps they went through to make their purchases, their reactions when the machines did not make proper change. Like all participant observers she operated with two purposes in mind at the same time.

James Spradley (1980) p.54