When one doesn't understand, one may react by going, "Eh eh eh.". Depending on how shocked/confused/zombie-like etc. the person is, they may add more length to the "Eh"s.
Girl 1: "So like, today, I brushed my face?"
Girl 2: "EHHHHHHHHHHHH EHHHHHHHHH EHHHHHHHHHH EHHHHHHHHH EHHHHHHHHH. EH EH EH."