A cowboy walked into a bar and ordered a whiskey. When the bartender delivered the drink, the cowboy asked, "Where is everybody?" The bartender replied, "They've gone to the hanging." "Hanging? Who are they hanging?" "Brown Paper Pete," the bartender replied. "What kind of a name is that?" the cowboy asked. "Well," said the bartender, "he wears a brown paper hat, brown paper shirt, brown paper trousers and brown paper shoes." "Weird guy," said the cowboy. "What are they hanging him for?" "Rustling," said the bartender.
Q: What’s the difference between bird flu and swine flu?
A: If you have bird flu, you need tweetment. If you have swine flu, you need oinkment.
This is a joke with an example of onomatopoeia in it, and the majority of the humor comes from that.
The jokester here replaces the word treatment with tweetment because a bird says tweet, and ointment is rendered oinkment through the same process.
There really is such a thing as bird flu and swine flu, however, the unlikeliness of two words being able to be formed that match the noises and are both related to medical interventions is also sort of impressive. I can only think of one other medical word that ends with "ment", and which also is medical, and that is liniment.