Santa's Little Helper barrier, allowing the dog to understand Bart's commands, and consequently pass the obedience school. Santa's Little Helper has fathered several puppies. In "Two Dozen and One Greyhounds" (season six, 1995), he runs away to the dog racing track where he mates with a female hound named She's the Fastest. She later gives birth to 25 puppies and when the Simpsons cannot take care of them any longer, they decide to sell them; however, Mr. Burns steals the puppies and decides to make a tuxedo out of them. Before he does this, however, he becomes emotionally touched by them. This convinces
Helper dependent virus and capsid encoding DNA, plus helper DNA. Every cell that is successfully transfected with all three DNA fragments will produce the necessary proteins to produce infective viruses. These viruses will only have transgenic DNA encapsidated and therefore once they've infected a patient's cell, they will not be capable of reproducing. Helper dependent viruses can also occur in nature without being "gutted". The term satellite virus has been given to a large group of viruses that all require the presence of another virus to replicate. Many of these are plant viruses, but animal viruses can be seen in the case of