Mnemonics, up and down
The Simpsons theme. The "The Simp-" to "-sons" leap is a tritone up, and Danny Elfman wrote it that way on purpose, so the show would have a recognizable musical fingerprint. The other classic is "Maria" from West Side Story: a rising tritone on the first two syllables, resolved up a half step on the third. The resolution is the point; the tritone wants to move, and Bernstein gives it permission. Rush's YYZ riffs on the interval in morse code if you want the deep cut.
Going down, no famous opening carries it, so use the descending button above. The interval's instability survives the flip intact, which is more than can be said for any other interval; falling or rising, a tritone is a tritone.
Jazz does supply a descending reference the pop songbook lacks. Mark Levine's interval table fixes the ascending tritone to Joe Henderson's "Isotope" and the descending tritone to the bridge of Ellington's "Sophisticated Lady."
On the staff
Why it can't settle
In C major the only naturally occurring tritone is F against B, fa against ti. Sing them together and your ear immediately wants F to fall to E and B to rise to C, the two tendency tones discharging in opposite directions. That outward resolution is what every dominant 7 chord is built around: C7 contains the same tritone between E and B♭, and when it resolves (E up to F, B♭ down to A) the chord lands on F major. Every blues turnaround, every II-V-I, every classical cadence runs that move. The dominant 7 is the engine; the tritone inside it is the spark.
Its rarity is a feature too. The tritone occurs exactly once in any major scale, which makes it a landmark: hearing where the lone unstable interval sits is part of how the ear locates the key in the first place. And because the interval splits the octave exactly in half, it's the only one that inverts to itself. Six semitones up from C is F♯; six more and you're home.
The "devil's interval" thing
You'll see the tritone called diabolus in musica in most popular write-ups. Medieval theorists did use the phrase, but as a teaching aid for avoiding awkward melodic leaps in chant, not a metaphysical prohibition. Nobody banned the interval. Renaissance composers used it constantly, just with the resolution worked out.
The cultural association with darkness comes from how useful the tritone is for tension. Black Sabbath built a sound around it. So did most horror scores. The interval isn't evil; it's the most efficient way in tonal music to make a listener feel that something needs to happen next.
What it gets confused with
The tritone sits between the perfect 4th (one semitone narrower) and the perfect 5th (one semitone wider), and in practice the confusion runs mostly one way: people mislabel a tritone as one of its stable neighbors, rarely the reverse. The 4th feels folk-friendly and the 5th feels settled; the tritone feels like you stopped a semitone short of safety. That unease is the giveaway. If the interval makes you want a next note, you've found the weird one.
How Aubel handles it
The tritone is the last interval to unlock. By then you've worked through everything around it, and the recognition question becomes "is this the unstable one?" instead of "what is this?", which is a much faster decision. The detail screen leads with The Simpsons and keeps YYZ for the Rush fans.