How can the presence of a fetal heartbeat in an ultrasound after 8 or 12 weeks be explained, despite the ensoulment only occurring after 120 days?

A distinction should be made between plant life, which concerns growth and nutrition and is found in inanimate objects and the fetus before the ensoulment, and animal life, which is associated with ensoulment and represents sensation and voluntary movement. The involuntary movements of the fetus and its heartbeat do not indicate ensoulment, but rather its growth like a plant. The soul is not breathed into it until after forty days, and its presence is known by voluntary movements.