Have you ever accidentally created a death trap?

I've had a big bucket full of rainwater on my deck since the last rain a month ago. I've been slowly using it to water my container plants, and so the water level has been going down.

This morning, I looked in the bucket and saw the waterlogged corpses of two mice. It seems that they went in there for a drink in the night since everything is so dry recently, and weren't able to get out since the water level is rather low. If it was just one, I'd call it an accident, but two is a pattern.

I've placed a big stick in there so that any creatures that wander in can get out, but it was still unfortunate that they died so needlessly. It's a big reminder that I need to be thoughtful of how resources I leave outside might be interacted with. In this case, it took them dying for me to be aware that such a thing was possible, but going forward I can avoid it.

Sadly, yes. I buried a round horse-trough to ground level for the coyotes to drink. Unfortunately, this was a death trap for about 50 baby quail. I felt horrible! By lowering the surrounding soil about 8" from the lip of the trough-pond the babies couldn't fall in and the deaths stopped....
Until it happened again! This time beautiful native grasses grew up around the pond to about 2' tall. The grasses concealed the pond from the juvenile quail who would flush when threatened then fly over the grass to their deaths. Another 50!!! Horrible! I removed the grass and things seem okay for now. I buy quail food as a sort of penance for these "learning experiences."
P.S. Your mouse story sounds like someone could be using rodent poison near you. One of the symptoms of poisoning is thirst. Your pets and/or other wild animals could have eaten those mice and also needlessly died:
https://vet.purdue.edu/addl/news/rodenticide-revolution.php
Maybe having water out can enabled you to safely dispose of the rodents so other animals could not eat them. You may have saved a coyote, raptor or beloved pet with that water Malek!

Right next to the bucket of water is a container of dirt and compost that I put food waste in. I imagine they were probably just scavenging from there, went for a drink, and got stuck.

The really morbid thing is that last night I went out and transferred some water from it into my watering can and used it on a plant (thankfully an outside one). It was dark, so I have no idea if they were already in there when I did. If they had been alive, I suppose I would have noticed.

I used to have a cat that liked to wait on the stairs and attack/trip you up as you passed. Does that count?

Yes as well. Far too easily, just like you did, rainwater collecting in a container (not intentionally).
Have found drowned mice, chipmunks, and a squirrel. I tend not to feel terrible about the mice, but those other guys, a bit.

Another consideration is reducing the standing water as a breeding ground for mosquitos. It is a different sort of death trap...
We keep seeing more West Nile virus, and EEE reports every summer in our area.

I hope to do better this year, but it will take some deliberate effort. Turning over pails, barrels, wheelbarrows, etc... they tend to be scattered about...
Perhaps a storage structure to keep the rain off and collect it in a screened off rain barrel. Also some bat houses.

I've accidentally created something that could've been a death trap. I got a free IBC (intermediate bulk container) that formerly contained molasses and just needed washed of the bits that didn't drain out. Somehow, the lid got left off overnight. I kept hearing weird sounds all night, but didn't think to go check. In the morning, I found a very upset and sticky raccoon in there. I put a branch down the hole in the top and they were able to climb out on their own. Had I not checked, that could've ended very, very badly for the raccoon. Hopefully they were able to clean themselves off and the molasses didn't cause any skin or other health problems for them.

I have accidentally created a death trap for some stink bugs. I was keeping an old pine wreath with my kindling to add to the fire at some point. One night, I tossed it in. Probably a hundred stink bugs fled from the fire, some crawling whilst on fire and others making terrible sounds as they caught fire and popped. I know they're invasive, but it still felt awful. It definitely made me wary of ever leaving a brush pile outdoors for any amount of time and then burning it where I left it.

Yes, I caught some tadpoles with the kids and we put them in a big plastic tub half full of water. The sun shone down later in the day, and cast shadows of the tadpoles on the wall of the tub. That attracted chipmunks, and we found 3 or 4 of them drowned before I realized what was going on.

I have a bridge crossing a drainage slough on my property and after a few years of open access I closed the gate on it.  The next day a deer fawn had been taken down by coyotes at the gate..

Confession time.
As a child we had a lovely big ornamental pond with fish. The goldfish had babies. I fished out some of those babies and kept them in a bucket. Two days later they were dead. I think they suffocated from lack of oxygen. We definitely were not supposed to be fishing in the pond, and I still feel guilty about killing them. I was probably nine.

Another death trap I made more recently is my home made vole guards. I use cut down 2l fizzy drink bottles (not something we drink, but I asked my customers to bring their empties in for me) Placed around the baby tree and tied to a stake they work really well at keeping the voles away. However I learnt that it is important to keep the grass from growing up around them too much. More than once I found not one, but a whole family of dead shrews in one. I think they get in by climbing up the grass, then can't get back out. Their family hear their distress and come in to rescue them and they all get trapped. I find the inside of the bottle flattened with mud and no growing things just dead little corpses. I'm glad that I have fewer trees to plant now and am more careful about keeping the grass back so the small creatures can't climb in.

I've heard that you need to be careful when putting out slug traps, since other small crawly creatures like ground beetles may fall in and drown. Again putting the lip a half inch above ground level stops most insects, but slugs can just climb in and (hopefulyl) die happy.