Here is the referenced xkcd
fluffy: Hee hee, I know, I could do a comic about Mussolini… where the trains are using time as fuel. [Shoveling clocks?] And then he’s all “That’s not what I meant!”
fluffy: I’ll save this for when I have time to draw.
[[One week later]]
fluffy: Oh hey, a new xkcd… “Thyme?”
xkcd: “Corns, leaves, spices…” “Spices? Really?” “Sure– Mussolini made the trains run on thyme.”