Tuck travels quickly through the bloodstream because Jack's heart rate has increased from being pursued by some villains. Tuck tries to stop his vehicle and avoid entering the heart through the tricuspid valve, which could be fatal to Jack.
Beakman answers quick questions about blood, veins, and their functions. They demonstrate this by having Josie dress as a "cell" and she goes to a restaurant where "blood" is the waiter that offers her food first and then takes away her waste to the kidneys and lungs. Then they have a germ come in and try to get close to the "cell" and "blood" comes in a cap and gets rid of the germ.