Harry: She needs help.
Bob: So did the scorpion when he asked the frog to carry him across the river, and we all know how that turned out.
"The Scorpion and the Frog" is one of Aesop's Fables. The scorpion convinces the frog to carry him across by reminding him that it was against the scorpion's own interest to kill him. The scorpion was unable to overcome his own nature, and stung the frog, dooming himself to drowning.