1. If you're foil baking fish - fold the foil packet over more than once.
2. Foil in the oven at 350 for 20 minutes gets hot.
3. Foil is suprisingly floppy, especially when being handled with slightly burned fingers.
4. Cleaning the bottom of the oven regularly is more important than you might think.
How did I learn all of these things you ask? So I put my fillet of cod onto the foil added some butter and folded it (only one fold on each side, see #1) and put it on the rack in the oven. Twenty minutes later I went to remove the packet and thought well I can probably just open one corner to check doneness if I can go quick (see #2). Burned fingers later I decided the fish was done and started removing the foil with a hot pad (see #3 otherwise known as - hello use a cookie sheet). As the fillet moved around in it's foil containment it all slid to one side and that corner came unfolded, so melted butter was dripping into the bottom of my oven. I stopped at this point, and reconsidered my options, and got a spatula and plate to finish this operation. However, the fish had slid enough that when I next picked up the foil pouch all of the fish slid out the other end. Onto the bottom of my oven (see #4). Hrm. I picked pieces of fish out of the bottom of my oven with a fork, trying to get as little bottom-of-oven-gook as possible in the process (everything on the bottom of your oven was edible once, right?). I put the fish into a collander and rinsed said gook away and then ate it anyway cause I'm stubborn like that. It was still surprisingly edible and even kind of good. And I cleaned out my oven.