The shadow thing refers to a North American tradition:

en.wikipedia.org/wiki/Groundhog_Day

Groundhog Day is a tradition observed regionally in the United States and Canada on February 2 of every year. It derives from the Pennsylvania Dutch superstition that if a groundhog emerges from its burrow on this day and sees its shadow, it will retreat to its den and winter will go on for six more weeks; if it does not see its shadow, spring will arrive early.