Why dogs don't laugh at human jokes

Dad has a joke he tells sometimes, just to be irritating, I think. Three legged dog - that means the dog only has three legs, not that is his name is Three-Legged Dog - although I guess it could be, 'cause no one seems to know what the dog's name is, and names are important to a dog. Anyhow, three legged dog walks into a saloon - OK, I don't know if you know how hard it is to walk on three legs, but the dog isn't going to just walk in. Try walking on one leg and you'll see what I mean - there has to be some hopping in there somewhere. OK, three-legged dog walks into a saloon - I hope you know what a saloon is, cause I don't. Dad says it is like a bar - well OK, I don't know what a bar is, either. Mom says, "Just think of it like a restaurant, but with no food and only things to drink that you can't have. Yeah - I know what a restaurant is. They are great places where Mom and Dad go inside and they come out smelling great and they have little white boxes of treats that they got while they were in there. I wish I could go in one sometime. OK - Saloon - bar - drinks I can't have - that clears it up. OK, Three legged dog walks into a saloon and sidles up to the bar. OK bar, again. Mom says a bar can be where you get drinks that I can't have, but it can also mean a thing like a tall table. OK gotcha. And people wonder why dogs aren't that interested in learning English as a second language. Right - Three legged dog walks into a saloon and sidles up to the bar. He stares at the barkeep... OK, wait, is this 'bar keep' or 'bark epp'? I guess it must be the guy who takes care of the tall table - other wise, I get the 'bark' part, but what's an 'eep'? Anyhow, Three legged dog walks into a saloon and sidles up to the bar. He stares at the barkeep and drawls, "... - OK wait, what is a drawl? Is that like a drool? 'Cause I have found out that most people aren't too crazy about drool, in spite of its obvious good qualities, so if he drooled at the barkeep, no wonder dogs can't get things to drink in bars. OK, Three legged dog walks into a saloon and sidles up to the bar. He stares at the barkeep and drawls, "I'm lookin' for the man who shot my paw"? And then Dad, and every one else laugh. Why do people think that is funny. I don't get it! If I don't get it, Ungus sure won't. He just asked me what a sidle was.