The whole red penis of a dog may come out because the owner is excited or stimulated by other things. This may happen to male dogs. If the protruding red color goes away quickly, don't worry about it and don't be nervous.
If it is not taken back for a long time, or even the dog licks it, then it may be the puppy's genitals Infection or allergies occur. It is recommended to take the dog to a pet hospital for examination and timely treatment to avoid serious consequences.