Way back when, I used to work in microbiology. One of our favourite tricks when we were bored was to fill a rubber glove with molten agar and dye. When it set, we cut off the glove and left it where some unsuspecting person would come across it.

We were often a bit horrible given to practical jokes back then (1970s), but I also remember exploring an unused store room (fighting off giant cockroaches) and coming across a litre (or two?) of pure 100% Analar ethanol, which made for a merry lab-rat party (not drunk straight from the bottle) for all.