In the following video a cat is heard barking like a dog and when caught by surprise, then begins to slowly revert back to meowing. 

Some people online claiming to be animal experts say it’s not unusual for cats to bark occasionally, as the sound can be made by their vocal cords. The cat in the clip could well have picked up the sound from a local dog. They also noted that it’s unlikely the cat switched back to meowing, due to being caught, since it has no true agency.

Others see this as a sign of intelligence with a purpose, as to say, “cats are up to something”. You decide.