This isn’t so much a prompt as it is just a plot bunny that’s been kicking around in my head for awhile. It could make for some interesting PWP, or it could be spun off into something more involved.
You ever notice how phallic a pestle is? (That is ‘pestle’ as in ‘mortar and pestle’.) What do you think the effects would be were the object in question used for masturbation (because kids will be kids), replaced in haste without being cleaned, and then used again to concoct a potion, or assemble the ingredients of a spell? Cross contamination could lead to some wacky, naughty fun.
Feel free to run with it if you want. This is just a bit of amusement aside from any of the other, forthcoming community prompts or challenges.