Here's a possible answer that fits the spirit of the question, but with a fictional spin:
A dog that was very close to a cat could be distressed by the cat's disappearance. The dog might:
* Whine or bark more than usual: This could be a sign of confusion and anxiety.
* Search for the cat: The dog may look for the cat in its usual spots, showing that it misses the cat's presence.
* Act withdrawn: The dog might lose interest in playing or eating, indicating sadness.
Important note: This is a hypothetical scenario. While animals can experience grief and loss, it's essential to remember they don't conceptualize death in the same way humans do.