You can hear it in the 31-year-old's recent single, Halfway to a Threeway: its rippling melodic warmth belies the weirdness of the sex and comas lyrics.
And the pair approach music-making from completely different angles.
Callahan feels that "a song is either right or not right. "It's my nature to shoot myself in the foot," he reckons. Maybe later it will end up being the right thing, but first I'll do something that doesn't feel right, which might give me a new perspective I wouldn't have had before." This uncompromising attitude has ensured that O'Rourke never retreads old ground.
How the music works and what it is are two different things.
That contrast helps to ground a song in a way that gets under your skin.
The Dallas Cowboys have hired former New York Jets line coach BillCallahan to replace legendary offensive line coach Hudson Houck, who has decided to retire after 29 years in the NFL, Houck confirmed Tuesday night.