It depends which two!

Head One:
Abby Hayes.  A bad haircut and a good mind.  At least, it's a good mind for some things.  I have good ideas for science fair projects (after consulting a lot of books in the library).

Examples:

1. How does water move through a leaf?
2. Do cats' eyes glow in the dark?
3. What causes dew?

Head Two :
Casey Hoffman.  An ordinary haircut and an evil mind.  Proof of evilness: constant jokes about my hair.
Example:

"You must be hair-brained!"  Laughs.  "Ha, ha, ha.  Get it?"

Other proof of evilness: his science fair project ideas.
Examples (there are millions):

1. He wants to study different parts of the fingernail and toenail.  (Exciting.)
2. He wants to test our reflexes.  He throws cotton balls at my face, and everyone in the class watches me blink.  (Forget it!)
3. He wants to breed fruit flies and maggots on decomposing bananas.  (Ugh! Ugh!  UGH!)

Final ultimate proof of evilness:

He calls me "Hayes."  And pretends to sneeze when he sees me.  "I have Hayes fever," he says.  "Ha, ha, ha.  Get it?"

These two heads are not better than one.  They cancel each other out.  We spent the entire hour arguing.  We have not decided on a science fair project.

If I don't do the science fair project, I'm going to get a really bad grade in science.  If I do a last-minute science fair project, I won't get the extra credit that I need.

And it's all Casey's fault.