1. This teacher who should have known better than to leave:
"Our teacher had shown us that the tiniest slice of potassium can fizz around water when she was called out of the classroom. The class clown decided to recreate this cool little experiment. Wanting a larger reaction, he took a chunk the size of a baked bean and threw it into the water. It exploded, shattering the huge glass bowl it was in, sending water and glass everywhere. The entire class sat in silence for a second, then the smoke alarm went off and the entire school had to evacuate to the field."
Submitted by dsw62
2. This inevitable explosion:
"In one biology lesson we dissected sheep lungs. The teacher had the idea of ‘borrowing’ the physics teacher's bike pump and using it to pump the lungs up to show how they would inflate in a live animal. Of course, he ended up overpumping and the lung EXPLODED with the whole class (who were crowded round the table) showered with bits of dead sheep and blood."
Submitted by rosieh47c50ef01
3. This not-so-gold ring:
"Our teacher wanted to show us that gold can't be dissolved in normal acids. One of my classmates didn't believe her, so she brought some sulphuric acid and threw her recently received and apparently very expensive yellow gold 18k engagement ring into it.
Seems her then-fiancé didn't quite tell the truth about the ring being gold. The ring was gone faster in the acid than she could look. And we all screamed when she launched her hand to try and fish it out – thankfully she realised what she was about to do."
Submitted by hellarobot
4. This proof that teachers should be careful what they say.
"The teachers once told us that the tables were flame-proof, so we turned the bunsen burners upside-down and found out he was very wrong."
Submitted by Bethany Markham-lee, Facebook
5. Why you should always clear up spills:
"In third year at university I accidentally set a petri dish of ethanol on fire. Unfortunately, earlier in the class the ethanol had been spilled on the paper bench cover, so everything on the lab bench went up in flames. Believe it or not, I now have a degree in Marine Biology."
Submitted by Rosie Britain, Facebook
6. This series of unfortunate events:
"I accidentally lit my lab notebook on fire while doing an experiment. In the process of trying to put it out, I broke a beaker by elbowing it off the counter and almost set the printer on fire. My teacher now tells that story as a cautionary tale to pay attention to what you’re doing."
Submitted by C6H12O6
7. This obvious outcome:
"Our chemistry teacher decided that test tubes could stand up on their own and filled one with some kind of acid. It spilled all over her desk and all she did was look at it and say 'Oh… it fell'"
Submitted by hahahaleema
8. This lucky escape:
"My friends and I would fill our mouths with gas from the taps on the desk and breathe it out over a lighter flame. Nothing bad ever happened, luckily, but it’s such a dumb thing to do!"
Submitted by Catybrady
9. This unusual punishment:
"After chemistry experiments we would always tip the leftovers into the classroom plants for no other reason than we were bored and wanted to see what would happen. When our teacher found out he sent us out onto the field and made us do the ministry of silly walks from Monty Python."
Submitted by Katthebamf
10. This lesson in paying attention:
"We were heating crude oil to a certain temperature, and I was too busy using the thermometer to figure my own temp out to check the experiment. The boiling crude oil exploded, shooting into the air, hitting the overhead light and causing half of the shitty foam board ceiling to land on my desk and all over my teacher."
Submitted by CCLBARLOW
11. This kid who got what he deserved:
"We dissected rats for an anatomy class. This one kid started jumping rope with the small intestine, which was disgusting in and of itself, but then it split. Feces on the ceiling."
Submitted by katloomis
12. This disappearing teacher:
"In chemistry, we were specifically told not to mix two chemicals. One kid did it 'accidentally’ and it made a small cloud of smoke which quickly grew until we couldn’t see anything in the classroom. We only heard the teacher say 'fuck this' and the door open and then close."
Submitted by alicep452d37610
13. This pair who got the last laugh:
"There were only eight of us in physics class and we were using Bunsen burners and digital thermometers. My partner and I were given the old mercury ones because we were always joking around and our teacher was afraid that we would break them. The other three pairs managed to set the string attached to the digital ones on fire and one pair even crushed their replacement Mercury thermometer. We stood watching feeling smug! So, in total, they broke four thermometers and then had to take turns with ours."
Submitted by laurad4169b4382
14. This extremely predictable outcome:
"I would burn anything in the Bunsen burner, from pieces of my hair to pens, rulers, my work and my friends work. And then I got banned from using a Bunsen burner for the rest of my time at high school!"
Submitted by oliviacliveb
15. This ghost cow:
"When my mom was a kid, she was in class doing cow heart dissections. Apparently a boy near her waited until another girl had just pressed the scalpel to the heart and he let out a low "Mooo". It must have been very convincing because the girl screamed, and threw the heart across the room – hitting another girl in the head."
Submitted by Josh Weston, Facebook
16. This important chemistry lesson:
"Electroplated a ring which was an expensive and precious family heirloom in copper and then proceeded to ask how to undo it. You can’t."
Submitted by Leah51
17. This worrying lack of attention:
"We were using bunsen burners and my friend didn’t understand how to properly adjust the flame level. He ended up breaking the bunsen, spilling gas all over the table, which then ignited and set the table on fire for a few seconds. The teacher never even noticed."
Submitted by cjt4a98a4ec6
18. This inevitable eyebrow casualty:
"Teacher demonstrated what not to do with a chip pan fire (i.e. add water). Flames hit and burnt the ceiling. So he did it again. I’m fairly sure he lost his eyebrows."
Submitted by bethanys44504cc7d
Note: Submissions have been edited for length and/or clarity.