This happened over 20 years ago. I was at the Heureka Science Centre with my kids. There was a microscope set up where you could look at bull sperm. Next to it was a sign that said, “Live sperm available from the guide.”
I turned to the gentleman standing nearby and asked, “Could we get some live sperm?”
He looked utterly horrified and asked, “What?”
I explained that we wanted to view live sperm under the microscope. He still just stared at us and repeated, “WHAT?”
I pointed to the sign — it said the guide would provide the sperm. Then he informed me that he didn’t work there — he was the bus driver for a school group. We quietly slipped away. Never did get to see those sperm.
English (UK) 
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