I was in one hospital ER for a kidney stone, but they had no urology available, so they sent me via ambulance ("thankfully", as a paramedic, one of our company benefits was that if we were ever transported, they'd bill our insurance and waive any charges to us) to another hospital. Ambulance crew wheeled me into the ER bay, where a 'transport' gurney from surgery, was waiting, and I slid from one to the other, and was wheeled to pre-op.
At no point did the ER staff ever talk to me. At no point was I in a room. Or in an ER bed, hallway or otherwise. Just ambulance, transport, and then to pre-op.
But, because the transfer physically happened in the ER, that second hospital tried to bill my insurance for an ER visit to the tune of $2,800 which I appealed (successfully, at least).