David Malki of the webcomic Wondermark explains the concept behind this shirt:
You walk around like everybody else, weaving in and out of the flow of humanity, searching fellow travelers’ eyes for the briefest flash of recognition — of coal-smoke leaking delicately from a too-loose collar, perhaps, or the deep churn of a furnace not baffled quite well enough, or of sparks leaping up in the hot space vacated by a man stepping off the curb and into the crosswalk. But now you can put an end to that timidity! Say it loud: Your lungs are boilers; your blood courses at two hundred twelve degrees. Your heart runs on steam power.
Product Page ($18.99-$19.99)