For reference, the dictionary definition of the word "pinto" is
Marked with spots of white and other colors; mottled; spotted.
It can also be used to refer to a piebald horse which has irregular patches of two colors such as this one:
For reference, the dictionary definition of the word "pinto" is
Marked with spots of white and other colors; mottled; spotted.
It can also be used to refer to a piebald horse which has irregular patches of two colors such as this one:
My guess is that "Jack" is a reference to "Jack the Ripper" because in the OVA, the main characters are chasing a serial killer. It could also be a reference to "Jack-o'-lantern" since the serial killer wears a pumpkin mask and is referred to as "Lantern".
On the other hand, the only two things I can come up with for Pinto is that it's a reference to (spoilers ahead):
1
The hidden bruises on the elderly patient which look like the spots of a piebald horse. The patient's skin was thus like a "pinto" horse.
2
The dual personalities that the nurse had because "pinto" could mean the she had spots of white (good) and black (bad).
I think theory #1 on the elderly man is more likely to be right than the nurse theory.