While they promise them liberty, they themselves are the servants of corruption: for of whom a man is overcome, of the same is he brought in bondage.  For if after they have escaped the pollutions of the world through the knowledge of the Lord and Saviour Jesus Christ, they are again entangled therein, and overcome, the latter end is worse with them than the beginning.  For it had been better for them not to have known the way of righteousness, than, after they have known it, to turn from the holy commandment delivered unto them.  But it is happened unto them according to the true proverb, “The dog is turned to his own vomit again; and the sow that was washed to her wallowing in the mire.”          2 Peter 2:19-22

See all of  2 Peter 2 and Proverbs 26:11.

A hog is still a mud wallowing swine, and it does not matter how clean you get one, and even tie a pretty bow around its neck; give it a chance and it heads to the mud wallow every time.

A dog will remain a dog, returning to its own vomit, even the house ones.