What does "cause raised eyebrows" mean?

Also, raise eyebrows. Cause surprise or disapproval, as in At school his purple hair usually causes raised eyebrows. This transfer of a physical act (raising one's eyebrows) to the feelings it may express took place in the early 1900s. Lytton Strachey used the term in The Eminent Victorians (1918): “The most steady-going churchman hardly raises an eyebrow at it now.”