In which a time traveller shows the historical artefacts he has collected

"And this is the very grenade that was used to blow up Hitler and prevent what would have been a second world war."

"But this grenade is still entact, how could it have been used to blow up Hitler?"

"And what do you mean it prevented the Second World War? World War II happened, it lasted five years and killed millions of people.

"Sorry, can I just take that grenade, I need to pop back in my time machine for a minute."