My 4 year olds mad questions!!!

Lol so my 4 year old is suddenly on a facination as to how he got into my belly. And how he got out lol. I palmed him off with..... you grew in there from a wee tiny egg into you. To then be asked. But how did the egg get in there. I replied with im not sure. But the tricky question is.how to answer to a 4 year old when they ask, how did i get out of your belly. Lol. Any mothers any suggestions on this one lol!!!