Eloi, Eloi
can easily be misheard as Eli, Eli.
There was a folk tale in Israel that Elijah would come to help the Messiah in his time of need. Presumably, this is what some of the people were expecting. If he really was the Christ then Elijah would come to his aid. The people did not realize that in the person of John the Baptist, Elijah had figuratively already come (see Mark 9:12–13). John the Baptist performed the same kind of ministry as what Elijah performed.
35 And some of the bystanders hearing it said, “Behold, he is calling Elijah.”