O Rose, thou art sick!
The invisible worm
That flies in the night
In the howling storm
Has found out thy bed
Of crimson joy
And his dark secret love
The throes of passion. Or a storm. A howling one. So the throes of passion. Blake did hold some fairly libertarian views about sex. 
 Those with sharp eyes– or well attuned ears– can pull out “worm” from ho w ling st orm .
The Sick Rose