I went to a wolf exhibit near Yellowstone, and caught them at feeding time. Someone asked why they don’t put live prey in for the wolves to catch. The keepers explained that the live prey—they would use rabbits—actually scream and make a lot of noise. They said that the wolves do sometimes catch the birds that are always landing in the exhibit.
It seems rather cruel to have a predator and not actively engage its predatory instincts.
Perhaps a solution for the zoo in Japan would be to coat the window so the lions cannot see out, but visitors can still look inside.
I did an internship at a science center with a zoo while in college. Even though I was in marketing, I was expected to handle other duties. I do know that feeding time for species requiring live prey was done after hours, to avoid upsetting the public. I never had to put live mice in the boa habitat but witnessed it a few times. I didn’t like it, asked if the mice could be sedated or something. Nature can be cruel.