And the answer for Blackie is…
Thank you all for your comments on this case!
Blackie was sent to surgery as the ultrasound showed a stick perforating the fundus of the stomach, and most of the stick was embedded in the adjacent omentum. The inhomogeneous appearance of the omentum supports regional inflammation/infection. The omentum successfully sealed off the foreign body, which explains why the dog did not display any gastrointestinal signs. The process was likely chronic.
Right after surgery, the heart rate returned to normal!
Please review the annotated video below: