Don't we have a rule against posting spider pictures?
Really? That seems silly.
It does, but I remember it became an issue once because a certain poster had a terrible fear of spiders, and it wasn't fair for him to randomly stumble across the pictures in a thread that is not explicitly about spiders.
No, we don't have a rule against posting spider pictures. We have a rule against trolling people, as in one guy saying "I'm deathly afraid of spiders and can't even look at them online" and then a couple people started immediately posting dozens of spider pictures in the thread he was already participating in to mess with him (which was the Thread Bombs topic, so not some small topic on a single obvious subject that one should be able to easily avoid).
Of course, on this board where nothing happens without being blown completely out of proportion, you can't even politely ask people to stop one time while not punishing or even threatening to punish anyone without it becoming a problem (not by you, by someone at the time) or it being misinterpreted as some kind of permanent board rule rather than a specific reaction to a single incident.