My pet theory is that in real life, the kid at the beginning of Jurassic Park who made fun of the 'six-foot turkey' never got a talking-to from Dr. Grant, and grew up to produce several of the movie's sequels.
Translated plainly, this comic reads "People who don't think feathered dinosaurs sound scary have never tried to fight an ostrich."
This comic is a jab at people who dismiss the idea feathered dinosaurs sound scary. Adding feathers to a reptile can trigger a cognitive dissonance; people today see feathers and think of harmless birds. However, the ostrich and a few other avian species, which are feathered dinosaurs (1211: Birds and Dinosaurs) are in fact deadly. The diagram points out that anyone who has tried to fight an ostrich would be scared of a dinosaur with feathers, and anyone who thinks a feathered dinosaur doesn't sound scary has never tried to fight one. The two groups of people are exclusive because the two circles do not overlap.
Ostriches are not typically considered scary or dangerous because its appearance is comical or awkward to most people; they are also herbivorous and not typically aggressive, choosing to use its great speed to outrun predators rather than fight them. In reality, however, ostriches are much larger than a human and will attack when cornered or when their family is threatened; their powerful legs can kick hard enough to kill lions and other predators, and their feet are equipped with large claws which can disembowel a human. Thus, the actual experience of fighting an ostrich would quickly convince any human that survives the experience that ostriches (and by extension other feathered dinosaurs) are, in fact, scary.
The title text refers to "Volunteer Boy", a kid in the beginning of Jurassic Park who dismisses a raptor fossil as a "six-foot turkey". Dr. Grant uses a fossil of a raptor talon to imply that a raptor would slice open his belly and eat him while he's still alive. This scares the kid into respecting the raptor. The title text theorizes that if he didn't get that pep talk, and continued to think of dinosaurs as "six-foot turkeys", then he would grow up to make some of the contested sequels in the franchise. Raptors play a central role throughout the series of movies, with some even being trained by a raptor handler like dogs.
Technically, the diagram is an Euler diagram, rather than a Venn diagram. A Venn diagram shows all possible combinations of two or more sets, including those with no elements, and so all of the regions must intersect in all possible combinations. An Euler diagram only depicts the non-empty combinations, and therefore does not have this constraint. However, this is a technicality, and many people use the words interchangeably.