Instructor: "There's been a change of plans. Instead of me teaching you the material science lesson, I got our resident MatSci expert to come teach you."
That instructor walks out.
Soon, another instructor walks in and closes the door.
New Instructor: "This was kind of last minute, so I haven't got a clue what we're doing. I hear you have a final tomorrow. Well, let's see... We can study for the final, meaning I'll go get a copy and we'll study it, We can blow something up, or we can get out early. What do you guys want to do?"
Random Student: "All three?"
New Instructor: "Sounds good. I'll go get the chemicals."
And such is how the morning proceeded.