This will help you avoid confusion with stem-changing verbs like "comenzar" and "encontrar" as the last vowel of the stem for each verb is "e" and "o" respectively. They are also known as "boot verbs"...This will help you avoid confusion with stem-changing verbs like "comenzar" and "encontrar" as the last vowel of the stem for each verb is "e" and "o" respectively. They are also known as "boot verbs" because this change is only for the subject pronouns "yo, tú, Ud., él, ella, Uds., ellos, ellas". The subject pronouns "nosotros, vosotros" do not have this stem-change. Moreover, the endings that need to change in conjugated versions are in blue.