Well, that's obvious. But what's not so obvious is that some components may look perfectly fine but act like Orville Redenbacher when in the reflow oven. Well, they won't actually act like Orlville, but rather, like his pop corn. Sort of. With popcorn, you can tell when it's popped. With a popped chip, you can't always tell right away.
Moisture sensitivity is a bigger issue with RoHS-compliant components, but can be an issue in leaded components as well. Even though the parts look like water-tight plastic, they really aren't. They do absorb  moisture and after improper storage, moisture-sensitive chips may popcorn or crack subtly underneath. This can create hard to find or intermittent defects. It is often more of an issue with prototypes because components are quite frequently consigned in partial lots. This may result in impaired moisture sensitive packaging or storage beyond recommended shelf life.
So, the message here is that if your parts are labeled as moisture sensitive, don't open the moisture barrier packaging before sending them to Screaming Circuits. Or, if you have to open the package, please let us know. We'll bake them at the proper temperature
Easy-Bake Oven: $25.99 from Hasbro
No. You can't use an Easy-Bake oven for your parts