Rubber Ducky

I've started taking baths again. That doesn't mean I haven't washed for a while, it's just that I've always preferred showering as opposed to wallowing in your own dirty water. However baths can be quite nice on occasion, so this morning, as I woke early and had no real reason to rush, I thought I'd run one. I went to put the plug in the bath, and stopped dead. It didn't fit anymore. It fitted yesterday, and the day before, and every day previously for the last 22 years, but today it's too small. THE PLUG IS TOO SMALL! I check I've got the right plug, I have. I check it's not the sink plug, it isn't. I double check it's the bath plug, it couldn't be more. I look to see if the plughole is gunked up with hair and muck, nope all clear. Yet somehow the plug no longer fits. It starts to freak me out, to really freak me out. Someone's broken in last night and ever so slightly enlarged our bath, or maybe they've shrunk the plug which would be easier. I decide I'm imagining it, so I run the bath and get in, but after a few minutes the water level has dropped below my... err thighs... and this is not all in my mind. I give the plughole one final rummage and find the strangest thing - an upside down lid, clear plastic, the exact, perfect, 100% precise fit of the plughole. To the millimetre man. It makes you stop and think. At some point we've bought some mystery product which just happened to be capped with a lid of portentous proportions which then somehow fell off when it was in or near the bathroom, rolled into said bath, landing upside down in the plughole, indiscernibly blocking it. What are the chances of that?