Roughly:
-add basis shape key and second shape key
-tab into edit mode
-select vertex edge loop (shift option click)
-scale edge loop (s)
-tab back to object mode. Changing value of Shape Key from 0 to 1 should make cleavage furrow move
-add key frame for beginning and end value of Shape Key
Watch this video https://www.youtube.com/watch?v=-pj1tS97N88
Roughly: -add basis shape key and second shape key -tab into edit mode -select vertex edge loop (shift option click) -scale edge loop (s) -tab back to object mode. Changing value of Shape Key from 0 to 1 should make cleavage furrow move -add key frame for beginning and end value of Shape Key