Leadup to latest Rental Inspection

Why do my cats always vomit when I clean house?  I woke to the sweet sounds of retching.  I gave gentle encouragement to Mary-cat to stay in the one spot and to please, please, vomit on the floor and not on an object. The time one of my cats vomited atop my flatmates black mesh entertainment stand and it dribbled through into the television and dvd player is still vivid in my memory.  They are not used to vomiting these inside cats.  They fight against it.  No history of habitual grass chewing and purging behind them.  She tries to swallow it down as it comes up and chews on the remnants like a ruminant.