One main goal of requirements engineering is ensuring that all stakeholders share the same vision of the future system. Vision Videos can be used for this purpose. They visualize the product vision at an early stage of the project. However, some functional aspects, such as an access code being valid only once, are difficult to visualize. Short texts could be a low-effort solution to complement videos with additional information. Thus, represented visions and requirements could be taken to the next level of clarification. Our question is two-fold: What effects do texts have in vision videos? What are suitable ways to add textual information to vision videos? We conducted an eye tracking study to investigate the effects of adding short texts to vision videos, either below the scene or as text overlays. We evaluated these two methods regarding video comprehension, reading time, cognitive load and subjective preference. Our study shows that texts in vision videos improve vision comprehension and thus support the achievement of one requirements engineering goal. Both methods increase the cognitive load of viewers only by a reasonable margin. No clear-cut preference for a single variant was found. We derive recommendations on how to add texts to vision videos.