I don’t understand this joke...

Can an old man make a young girl get pregnant soon after getting married?

---No!

Why do young girls get pregnant?

---Because the person who made the young girl pregnant was not the old man, but someone else!

Can an umbrella kill a rabbit?

--No!

Why did the rabbit fall to the ground?

--Because someone else shot him!

The most critical sentence in the conversation with the doctor, "Someone must have fired a gun next to me," actually implies to him that someone else did your wife's pregnancy and she is pregnant with someone else's child! Having an affair with someone outside!

Tidying up the snow without cold