Two scientists walk into a bar.... The first scientist tells the bartender he will have some H2O. The second scientist tells the bartender he will have some H2O too. Several minutes later, the second scientist is dead.

Two scientists walk into a bar. The first scientist says ""I'll have h2o"" The second scientist says ""I'll have a water"" The first scientist goes back home and rethinks his assassination plan.

Two scientists walk into a bar... The first scientist says to the bartender, ""I'll have some H2O."" The bartender nods and gives the man a glass of water. The second scientists says, ""I'll have some H2O, too."" The bartender nods and gives the man a glass of water as well, because he speaks English and understands that the second scientist, rather than requesting a drink which would kill him, simply wanted a glass of water in addition to his friend's.

2 Scientists walk into a bar... The first one tells the bartender, ""I'd like some H2O"" Upon hearing that, the second scientist says, ""I'd like some water too. Jimmy, we're not in the lab anymore...""