...
At the hospital: a doctor and a female patient...
Doc: "Hmm, well... it looks like you'll soon have more than one mouth to feed."
Patient: "R-really, doc? Are you saying that...?"
Doc: "...Yup, you've got pinworms!"
...but wait! Here comes the funny part:
Patient: "What? Then... what should I do?"
Doc: "Well,
Q: What's the difference between a pigeon?
A: None. Both sides look the same. Especially the left one.