Human Foils Operation Cat Vomit!

 Honestly, I don't know how the cat did it (and I have no idea which cat did it---they all fled the scene and are securely ensconced in their respective feline fortresses).

 

Cat vomit - Note interesting splatter pattern

 If you look at the photo, you can see that there's quite a large splatter pattern. If the cat was at the bottom of the stairs, it shouldn't have reached all the way to the riser of the 5th stair (not pictured). I mean, really, how could the cat have blown puke that high up from the bottom of the stairs? Using a blow gun? Perhaps a hand-held fan?

No cat vomit remains!

 

On the other hand, if the cat vomited from the top of the stairs, how did he or she manage to get the vomit on the risers? And there's no way the cat could have blown chunks from the second set of stairs as there is no access to overlook the first set. All I can say is, Bravo! Bravo, kitties! What massive talents you cats possess!

  Fortunately, all was cleaned up with Woolite with Oxy. I had to breathe through my mouth because of the stench and wear the rubber gloves because it was so juicy. But, no trace remains. 

 I am surprised the cats attempted such a brazen attack during daylight hours. Their previous efforts have yielded much better exclamations of horror and disgust by perpetrating this appalling act at night where the unwitting victim (usually always Gregg) steps in the mess when walking to the bathroom. Gregg has an uncanny 100% detection rate.

Better luck next time, you felines!