We often take for granted how difficult it is for actors to do their jobs. Imagine having to fake-cry in front of dozens of crew members, pretend to have sex with a co-star and make it look convincing, or imagine that a green tennis ball is actually a dragon.
It can be an awkward and nerve-wracking job, and as a result, real-life emotions can sometimes influence an actor's performance.
For instance, if a scene or a role is particularly intense, it requires the actors to get in a darker, stranger headspace, and this can have a direct effect on their co-stars, creeping them out and even scaring them with some unpredictable or intimidating behaviour. From maniacal clowns to imposing mob bosses, the actors who inhabited these ten roles were so invested in their performances that they genuinely scared some of their fellow cast members.
While this often leads to a more convincing scene, it can also have the unfortunate side effect - in some cases - of permanently damaging the relationship between the actors in question. This is why you should never punch people in the chest...