Updated at 11:35 a.m. ET
Bernie Sanders and Joe Biden are very much on each other's minds.
At his campaign rally in Philadelphia on Saturday, the former vice president went off script — twice — to deride a protester with a whistle.
"That must be Bernie or somebody," Biden apparently said, raising eyebrows and drawing laughs.
(The line is at 8:21 into this video. You can decide for yourself what he said.)