On one hand, I aspire to an Ivy League vocation:1 
 professor of the sciences in higher education. 2 
 But like noble amphibians that thrive on land and in the stream, 3
 I’ve got another world of which I like to gladly dream. 4 
 Some say that it’s abnormal; my affections are exclusive. 5 
 In science, they say, emotions are something quite elusive. 6 
 Line 3 exemplifies which kind of figurative language?