The speaker of "Porphyria's Lover" sounds awfully straightforward. His tone is incredibly reasonable, which makes it even creepier considering he's describing horrific things (such as strangling his girlfriend and cuddling with the corpse). He even makes it sound as though he was doing her a favor – he calls it "her darling one wish" (line 57). It's hard to tell from the speaker's language that he's off his rocker, since he speaks very smoothly and matter-of-factly. The rhyme scheme remains steady, and the meter is pretty regular (except for a few places – check out "Form and Meter" for some telling exceptions). What kind of psychopathic murderer would be able to describe his crimes so calmly? Thus, the calm, smooth tone of the speaker adds to the effect of the poem. The speaker is kind of like the killer in the movie Seven: he doesn't think he's done anything wrong, and that's part of what makes him so terrifying.