Other mistake: Ben brings Emily home from the hospital and Duke is in the back seat. When Ben stops and puts the car in park you can see in the background that the car is still moving.
Other mistake: Ben goes to meet a friend in Social Services. On the door, it says "Sevices."
Other mistake: When Ben is in the car with Emily, they pull to a stop and Ben shifts the car into PARK. However, the car is still visibly moving.
Answer: In the course of the film it's revealed that Ben has done extensive homework and taken drastic steps to find the right person, i.e. a "righteous good person" to give them what he has left to offer. Therefore, he would have to find someone with his own rare blood type AND needed a heart...which he eventually did.
CCARNI