This reminds me of Pope's lines from his "Essay In Criticism":

True ease in writing comes from art, not chance,
As those move easiest who have learned to dance.
'Tis not enough no harshness gives offense,
The sound must seem an echo to the sense:
Soft is the strain when Zephyr gently blows,
And the smooth stream in smoother numbers flows;
But when loud surges lash the sounding shore,
The hoarse, rough verse should like the torrent roar;
When Ajax strives some rock's vast weight to throw,
The line too labors, and the words move slow;


---The last two lines move marvelously slow.

It is difficult to say the word lugubrious with frowning...

hah! i suppose it does depend on your mood... but there are definitely some words whose order of letters just make it impossible to pronounce them quickly (if you're reading them out loud, of course).