What on earth happen???

Beware to those conservative readers...you are warned beforehand that this post contains uncensored picture..

I seriously do not understand how on earth did this happen. You'll be shock.
The bf, as usual attached this very amazingly cute pictue of two little kitties doing the Titanic stunt in one of his latest mail.

Being unaware of anything suspicious, I click on the exact mail few days later, to read the mail again, cause that was one of the most meaningful mail he wrote to me, and, imagine my shock when my cute little kitties turned into this very disgusting picture......
(and mind you people, the black coloured part, I drew it on my own, so that I won't be accused of turning my blog into some underage pornography section.
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Terrible ain't it?? I called up the bf immediately and ask whether he pulled a prank on me. He was dumbfolded. When he check back the mail, and to his utter horror, he saw this, he went nuts, cursing and scolding whoever, and whatever did this.
Up until now, we have discussed it over and over, yet could not come up with a proper explanation, to how did this happen....