You think every rule you have to provide to students in your syllabus came about for a reason. The special instructions you now offer before students go on a field trip came as a result of the adventure gone wrong. You still have flashbacks from that night at the Poetry Center and the performance piece where your student staged someone to heckle him, and then, like most play fighting episodes, something went horribly wrong.
You know this sign on the trail is a reminder of something like this.
And you know this sign is for more than lava; it is for every bubbling volcano you might meet on the city street.