My dog, Lilith, is the size of a puppy, but she never acted like a puppy. She's 2 years old now and weighs about 10 lbs...same size as one of my cats. She is a Rat Terrier, but she has long skinny legs like an Italian Greyhound. A victim of a breeder not knowing what they were doing. My mom got Lilith and her sister through the animal rescue stuff she does. Lilith's sister has congenital limb defects and can't jump/has poor muscle tone. Lilith can't jump either.
When I got her she would screech like some kinda demon at anything that bothered her (cats, paper bags, leaves that got too close, etc)...then she decided that she would screech at us if we petted her in some manner that she found incorrect. My partner and I spent a weekend passing her back and forth and purposefully petted her incorrectly until she got bored with screeching (and she saw we weren't doing anything nefarious by petting her).