As Sid creates his own rendition of a launch with his toys, he prepares to set Buzz Lightyear aflame. Seconds before he performs the task, he hears Woody, the toy cowboy, speak. Woody's confrontation scares Sid, as does the human-like behavior of the other toys.
Beakman explains what a vaccine is by acting like Edward Jenner. He explains how Jenner created the first vaccine using cow pox. Then Beakman uses a large ball (cell) with holes in it (receptors) and explains how viruses (a cube with pegs on it) attack our cells by attaching to the cell (pegs on virus go in holes aka receptors on cell). Beakman likens antibodies to cowboys ready to fight and explains how the immune system is normally triggered from a virus, unless that virus is too fast, then the body can't catch up. He then explains that vaccines work tricking the immune system into going ahead and making antibodies so that when you really do get sick, you can put up a better fight.