Ahem. Today’s SMBC contains a linguistics error.
There is no glottal stop in “pet dog,” “mint condition,” “rat trap,” “internet porn,” or “elephant gun.” Those are unreleased alveolar stops. I do think that there’s a glottal stop in “Bat Man.”
UPDATE: Language Log commenter Mike Aubrey comes to the same conclusion.
tompepinsky.com 
Neil Coffey May 11, 2012
The statement that these phrases contain glottal stops isn’t necessarily wrong. It just depends slightly on what exactly you categorise as “glottal stop” and possibly on individual pronunciations.
Ladefoged & Maddieson, for example, analyse a (British) English syllable-final [k] as “the entire velar closure is overlapped by a glottal stop” (p. 73).
So, does another stop with a superimposed glottal closure count as a “glottal stop”? I think that’s largely a matter of your particular analysis. As one LanguageLog poster commented, a deciding factor could be whether you think that the glottal restriction is what is ‘mainly’ stopping the sound.
Neil Coffey May 11, 2012
P.S. by “sound” I really mean “airflow”, of course 🙂
Tom May 11, 2012
I think that’s right–it is possible that these unreleased stops are accompanied by full glottal closures. But I don’t think that in general that’s how American English speakers produce most of these phrases (again, Bat Man is the exception). Certainly not rat trap!