What is it like to know two languages?

To all multilingual ones here, I pose this question: what is it like knowing multiple languages? Do you think in different languages, change when the environment does, or switch between them randomly? Do you ever get your words mixed up (i.e., you're talking to an English speaker but instead of saying cheese you say queso)? Do you find that knowing another language helps or hinders your understanding of your native one?

Pick and choose whatever you want to answer, but thank you for your time either way!

>>62
Yahoo's monolingual dictionary has an entry for 【突然変異体】 with とつぜんへんいたい given as the normal reading. One of the Homonyms it gives in the definition is ミュータント。
A mutation/突然変異 really is a sudden change/variation since it happens from one generation to another without intermediate steps, so I think the kanji aren't that bad a choice.

>>61
how many brush strokes something would require if you were to write it on paper is irrelevant in the computer age.