The first external force sal experiences is between Sal and Ben “did that taste like blackberries” this causes sal to like Ben and kiss him later on
The second external force sal experiences is between sal and moving “my father plucked me like a weed and we drove Euclid ohio” wants sal got to Euclid she started acting like a wild boar and then later on she sees her dad from her point of view
The third external force sal experiences is between sal and Mrs.Cadaver “what do you think happened to Mr.Cadaver“ this causes sal to believe Mrs.Cadaver is a murderer until Mrs.Cadaver tells sal how she met her father