I somehow got suckered into playing with Billy this morning. Someone (a human) told me that I owed him.
At least Katherine retrieved the laundry for me while I was busy. (She also retrieved Whitey, who went down to help her.)
In the midst of all this, I heard the semi-famous gurgling noise of Emily throwing up. I wasn't sure, but I adjourned playtime to the second floor so I could check the usual suspects, including my office, Katherine's office, litter box annex, and of course the bed. All clear, and Emily was sitting calmly on the bed, so Billy and I went back to playing.
Come to think of it, I found Emily sitting calmly the last time she threw up when I was around. Also like last time, she did throw up and I missed it. This time, she avoided immediate detection by hitting the far side of the bed, almost under (and on) clean clothes I had tossed on the bed to free up a laundry basket. She missed the clothes, but got both the bed quilt and top sheet.
As this is the fifth time she has thrown up in ten days, it is worrisome.