When using inversion (verb then subject) in questions, a -t- is placed between the verb and il, elle, or on for pronunciation purposes to make it sound pretty. This happens whenever the verb ends in a vowel (parle<-), but you wouldn't say, "Finit-t-il toujours ses devoirs?" because finit already ends in t.

"t'' we put between two vowels just for pronunciation. for ex. "Il a" but A-t-il? Il mange but mange-t-il? but we say Ils ont and Ont-ils?