The esophageal groove closes in response to milk proteins and the suckling reflex. The esophageal groove is in the reticulum at the end of the esophagus.
Jim Paulson, University of Minnesota Dairy Regional Extension Educator.
Source: 2005 North Carolina Dairy Quiz Bowl Junior Division Questions ( www.cals.ncsu.edu/an_sci/extension/dairy/4-H/quizbowl/quizbowlquestions.htm)