I stumbled across a post about 16 words that may not mean what you think they mean. While I knew most of them, I did learn a few things, including:
“Less is often confused with fewer. Use less to refer to quantities that can’t be counted and fewer to refer to numbers. There were less people in the office today is incorrect, because people can be counted. Instead say: There were fewer people in the office today.”
“Poisonous—often confused with venomous—means a plant, animal, or substance capable of causing death or illness if taken into the body. Venomous means capable of injecting venom. A rattlesnake is not itself poisonous, because if you eat one it won’t poison you. A blowfish will kill you if you eat it, so it is poisonous, but not venomous.”
And on a random side note, I found this while looking for Inigo Montoya images and it cracked me up how well it fit.