Why?
Perceiving is work done by the body and the brain, and consumes resources. Seeing more can be a greater strain in certain cases. Here, observing a hummingbird wingbeat by wingbeat means sampling the visuals at a higher rate than normally/humanly possible, i.e. doing more processing.
Even looking at a still image of a colorful hummingbird would mean more sugar burned than looking at a still image of blank white, although to a fairly insignificant degree. But sampling at hundreds of images per second is true extra work for the sensory paths involved, and doesn't happen for free.
Of course, the experience could be "fake" in many ways, and no extra effort would take place. And mindfulness, meditation or daydreaming sorta works: if you properly concentrate on doing less, you consume less of your resources. Perhaps the protagonists just went to sleep and had fancy dreams in which very little happened (i.e. everything seemed to happen very slowly)? This is the physiological opposite of actually observing hummingbird wingbeats in detail.
Timo Saloniemi