Evidence of unauthorized animal uncovered during inspection

[Wesley W.]

Hi folks,

My lease requires all animals to be approved prior to their being kept in the rental unit, and there is a one-time fee and additional monthly charge for each approved animal.

The subject tenant has approval for one dog in their unit.  During an inspection today, I observed a litter box (and evidence of its use) in the bathroom as well as cardboard cat food boxes in the recycling bin inside the unit.  I did not see a cat food bowl, nor did I actually see the cat.

I'm looking for feedback on my written communication to the tenant regarding this incident.  I'm considering a "Notice to Cure", but I'm concerned that since I did not actually see the animal, the tenant can just concoct a story about how he was "watching" a friend's cat (a violation, nonetheless) but that he's gone now.  I don't want to get into a "cat & mouse" game (pardon the pun) where the cat hides when I visit to follow up on this, and the tenant continues to deny its existence.  I'm struggling with how to write the notice without bluffing about me actually seeing the cat as well avoiding getting into the minutiae of my "proof", which may come off as creepy.  I'm wondering how others have handled the situation themselves, and how your notice toed this line on circumstantial evidence.