This happened to my friends and myself not too long ago during a game of Dungeons and Dragons we were all playing. We were using Version 3.5 rules, and I was playing as an Elven Druid. My character was also in the company of a Human Sorcerer and a Human Bard/Barbarian cross-class.
It is important to note that we have a house rule when it comes to Knowledge Checks: rolling a D20 to determine how much one knows of a particular subject. In our group, such rolls are made "blind" behind the dungeon master's partition so that only he, and not even the roller, knows just how good he rolled. We find that this makes for better role playing.
Now on to the actual story:
We were deep into the underground lair of an evil cult that has captured one of our comrades, walking down a long and twisting corridor. So far we had managed the journey with little incident, but adventurers never have such luck for long.
Up ahead we could hear the echoing of a loud hiss. We decided to continue forward cautiously, in case of ambush. Further ahead, we discovered a tattered and torn piece of snake skin. This, of course, meant that it was my job to identify what species of snake it belonged to, and to judge if it were a threat or not.