Bob is usually friendly and gentle, and is only aggressive towards the postman. He is intelligent, and is described as being "almost human".
- He barks at Bella when he spots her at the stair landing inserting the eyehook for the tripwire. This causes Miss Lawson to wake up and tell whoever it was to put Bob away. In the process, she saw "TA" on the dressing gown. In the original novel, Miss Lawson woke spontaneousy.
- Bob is given to Poirot near the beginning of the investigations shortly after Emily dies. The original plot device of a picture of a dog on a jar and the caption "Out all night and no key" as Bob is in the house during the accident.
- Instead, Bob helps Poirot in different ways:
- First, Bob has a trick of pushing his ball down the stairs, then running down the stairs ahead of it to catch it with his mouth and then brings it back to his basket. Bob keeps repeating this trick for Poirot until he realises that Bob seems to be trying to tell him that he always keeps his ball away in the basket after playing with it. Hence someone else must have moved and placed the ball on the top of the stairs.
- Later, Bob barks at his own reflection, leading Poirot to understand how "TA" becomes "AT" in a mirror. In the original, Poirot came to this conclusion after putting on Teresa's broach and looking at a mirror.
- At the end of the show, Poirot successfully hands Bob over to the Tripp sisters, claiming that he had a visitation from Albert, the Tripp's dead pet. Poirot says Albert told Bob to go and live with the Tripps.
In Témoin muet, the Les Petits Meurtres d'Agatha Christie adaptation of the story, the parallel character is named "Max" but this dog has a much smaller role than either "Bob" in the original novel or in the Suchet adaptation. His role as a "dumb witness" hardly used in the solution of the crime.