Follow the best advice ever given to a time traveler to the past. From Futurama's "Roswell That Ends Well", the Professor tells Fry - "Don't do anything to change the past, unless you're supposed to do it, in which case for God's sake don't NOT do it." Wise words.
I like the part about the butterfly. In that classic story, a guy steps on a butterly 65,000,000 years ago and the changes roll down through the millenia until they return and nothing has changed except everyone is a fascist and they can't spell.
One of Ed McBain's 87th Precinct novels tells the story of a perfect murder. The killer is a young man from out of town who impulsively kills a hooker, puts her body in a refrigerator and dumps it into the river. Then, after considering going into the police station, instead goes home, to mother. McBain ruined this later when is another novel the guy winds up coming back and confessing. I call wuss, and I'm not sure if I'm talking about McBain or his character.
Anyway, he committed the ultimate level of "perfect murder". Kill someone no one knew existed and will never be missed.
@Maureen "Is that classic trash". Like a lot of famous books it was trash when it came out, but it survived and is now a classic.
The thing "people didn't know" that has always baffled me is the circulation of the blood. People had been beheading people like forever and it took some guy to "discover" this? What did they think that stuff was - pesto?
On 10 Things I Believed When I Was A Little Kid In Order Of How Embarrassing They Still Are When I Remember Them Today
When I was a kid (1950's) they would announce on tv that "All aliens must register with the government each January". That was the most exciting thing I ever saw on TV. There were aliens on Earth, the government knew about it and it was okay for us to know about it. I never saw one, but I looked. I was so disappointed when I found out what they were talking about. I still believe though.