A、The songbirds have transparent legs. B、The songbirds dance very quickly. C、The songbirds often hide behind the leaves. D、The s

(l)Scientists have discovered the species of songbird that performs a tap dance so fast that it can’t be seen by the naked eye of human beings. Researchers from Japan and Germany slow down footage of the blue songbirds during courtship. Here’s our science reporter Jonathan Web. "Now, they’ve discovered that tap dance is in the course of courtship of both male and female blue songbirds. This is very obvious in the process of the songbirds expressing love to each other.(2)The next step for the researchers is to discover the relationship between courtship and this fancy foot work, such as whether the birds mate is courted by the sight, the sound or the vibrations of this fancy foot work. Such is the agility of the songbirds show stopping quickstep that could only be fully appreciated in super slow motion." That’s the latest BBC news.
1. Why does the naked eye seldom see the dance of the songbirds?
2. What should the researchers do next?