"You have a spider on your face!"
Translation:Máš na obličeji pavouka!
Czech is cheap when it comes to use of possessives. English uses them everywhere. If you can use it in English, do so. One way to avoid articles. To a czech ear using 'tvém, svém" sounds little silly. Like who else"s face would I be talking about when I start the sentence with "You have...". Of course it is yours. And so we typically do not say it.