Professor Frank Baxter and some animated friends answer questions about blood. what makes it red? Why do little animals' hearts beat so quickly? And so much more.
| Actor | Role |
|---|---|
 Frank BaxterHimself | Himself |
 Richard CarlsonMr. Fiction Writer | Mr. Fiction Writer |
 Mel BlancSquirrel / Turtle / Alligator / Rabbit (voice) | Squirrel / Turtle / Alligator / Rabbit (voice) |
 Sterling HollowayLab assistant | Lab assistant |
 Marvin MillerHemo / Professor Anatomy | Hemo / Professor Anatomy |