Er, whoops.

Artist comment explains:
 
“Ah… remember that time when Twilacus were about to… er… never mind. [link]
 
Anyways, Spike went round to Rarity’s, hoping that he might perhaps get a cushion to lie on, when…
 
Rarity had been thinking about LURVE and issues she had had with it. Namely, all the handsome stallions she had fancied either turned out to be chauvinist pigs (i.e. Prince Blueblood) or oblivious and ergo uninterested (i.e. Fancypants). She dwelled on this for a while, and then realised that she would have to compromise on appearance if she was going to get the male of her dreams… then she remembered who followed her around and did WHATEVER she asked him to. Rarity was shocked with herself for considering romancing with a dragon… but over the next half hour, she started to come to a sudden realisation (yes, another one - she was on a roll tonight): “Oh noooo!! My true love is a reptile, aaaaaaargh…”  
So there she was, drowning her sorrows, when who should come to the door but… Spike. Oh. Bad timing. (Or, depending on your point of view, exceptionally good.)
 
Oh! I can draw Spike now. And Rarity’s tail.”