As we are on the topic now... I'm pretty sure many bees have encountered problems with stuck stoppers. What I see most ppl doing is trying to turn around the stopper, so it might get loose. Wrong thing to do! It will only get stuck harder. The following picture should illustrate what you'd have to do:
Do not turn around the stopper, just wiggle it a bit to the left and to the right. Don't use brute force. Think you're giving a nipple masage. Do it gentle and with care. Eventually, the stopper will give up its life as stucked-stopper and come out. It can take a while, so you are warned. Don't tell me this is bogus because you have been trying it for more than 5 minutes. It can take a while... My record is ca 20 minutes! A stoppered flask containing 10% KOH, unopened for over half a year... but the stopper gave up
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