One episode is
not a diagnosis.
A video can show a dog turning toward its tail. It cannot, on its own, establish why the dog is doing it.
What the clip leaves out
Did filming begin after the behavior started? What happened before it? Has the dog been chewing the area at other times? Does this interfere with eating, rest or play? These questions do not turn the owner into a clinician. They make the limits of a clip visible.
VCA describes physical problems that can resemble or contribute to compulsive behavior. AAHA explains that new, intense, hard-to-stop or injurious tail chasing needs veterinary attention. Neither an entertaining appearance nor a single interruption can safely exclude those possibilities.
VCA: Compulsive Disorders in Dogs · AAHA: Why do dogs chase their tails?
Keep observation and theory in different sentences
Compare 'the visitor made him anxious' with 'a visitor entered; spinning started; I wonder whether the arrival mattered'. The second account gives the professional something to assess without treating an interpretation as a fact. It also leaves room for physical causes and other contexts.
Make uncertainty useful
The worksheet uses three duration states: measured, estimated and unknown. It asks whether you saw the beginning and what the dog did afterward. A missed start is not a failed observation. It is information about how much weight a record can carry.
The context-map example on this site is fictional. It shows why two episodes after a doorbell do not prove a cause. Do not provoke more episodes to test a theory or capture a better clip.
Do not postpone help to finish a record
Notes are preparation, not permission to wait. If your dog is injured, distressed or showing worrying changes, seek veterinary help. Bring what you have, including the gaps. The professional can tell you what information would be useful next.