えーと (or えっと) is the standard Japanese filler 'umm / uhh.' 頭文字 ('head letter') means 'initial, first letter of a name.' とる is a dialect/gruff spoken contraction of ている (common in western Japan and gruff masculine fiction). わい is an old-fashioned masculine assertive sentence-final particle — used by older men or for comic grumpy-old-man effect. The comedic beat is that the second speaker interrupts before the first can even finish guessing.