The trick is the two ways it can be understood; read a line at a time, or read from the middle of one line to the middle of the next.
I Saw a Peacock, with a fiery tail,
I saw a Blazing Comet, drop down hail,
I saw a Cloud, with Ivy circled round,
I saw a sturdy Oak, creep on the ground,
I saw a Pismire, swallow up a Whale,
I saw a raging Sea, brim full of Ale,
I saw a Venice Glass, Sixteen foot deep,
I saw a well, full of mens tears that weep,
I saw their eyes, all in a flame of fire,
I saw a House, as big as the Moon and higher,
I saw the Sun, even in the midst of night,
I saw the man, that saw this wondrous sight.