In the South Park theme song, Kenny says, “Mmmph mmmph mmmph mmmph!” since he’s muffled by the parka hood he’s wearing. The lyrics are meant to be unintelligible, and this is a running joke in the show.
In the South Park theme song, Kenny’s muffled line occurs during the part where the other characters sing:
“Whatcha gonna do when they come for you?”
Kenny’s part is usually just him muffling words under his hood, but the line is actually, “I’m gonna die, die, die,” referring to his frequent and often absurd deaths in the series. The theme song itself is a parody of the song “South Park is the Place to Be” from the show’s opening sequence.