One of those party guests is the furiously prolific Jill Goldston. I added her to the cast list of this film on the IMDb.
You've seen Guy Standeven in something because the man was in everything.

How? As glenmusher stated, it's Zarkov's memory of the event. So in reality, when his wife drowned, no one just stood around watching. How it actually happened, we don't know. Perhaps she cracked her head when she was thrown in. Perhaps she wasn't literally thrown in, but accidently pushed and no one noticed until it was too late.
The idea is that it's not truly his memory, just his emotional reaction of the memory. Most importantly, the feeling that it was his fault.

Still seems pretty f'n stupid.
I want the doctor to take your picture so I can look at you from inside as well.

Remember it's Zarkov's memory of the event, not necessarily how it happened, mixed in with his feelings of guilt, sorrow and helplessness about it.
Everything will be OK in the end, if it aint OK,it aint the end.

I always wondered about that scene. Makes no sense at all.