Study the structure of the following sentence.
When I extend my arms, thou extendest thine; when I smile, thou smilest in return; when I weep, thou weepest; but when I try to clasp thee beneath the stream, thou shunnest me and fleest away!
The basic structure is "When I do something, you do the same thing." This pattern is repeated twice, for a total of three things -- "extend," "smile," and "weep." Semicolons separate the three examples. The semicolon after "weepest," however, is followed by a "but," and then the pattern varies to "When I do something, you do something different." Note also that in this final section, two verbs are used ("shunnest" and "fleest").
Write a sentence that imitates the pattern. You do not have to use "I" and "you," but you obviously do have to use two different living things. The following is another example.
When the cat chased a moth, the kitten attempted to do likewise; when the cat washed her paws, her baby imitated her; when the cat jumped on the table, her kitten did so too; but when the cat let me pet her, the kitten bolted and ran into the bushes.