As soon as I saw the words "rotten egg," I thought hydrogen sulfide, sometimes called sewer gas. Hydrogen sulfide can be dangerous and is quite common in oil refineries. Here in California, a worker was overcome by H2S. He and another man who tried to rescue him died.
Go to Wikipedia and read about the hazards and effects.
Hydrogen sulfide exposure should never be taken lightly.
I hope Geela's doctor finds she's alright. It is bad enough that she has to put up with a moose.