Here is another classic that I couldn't find anywhere on the site:
A man is lying dead in a field. Next to him there is an unopened package. There is no other creature in the field. How did he die?
My notes to try and avoid this being too broad:
The man died where he lies. He was not moved to this spot. (He wasn't shot, stabbed, poisoned, etc.) Nothing happened earlier in the day to cause this death to be expected.
He did not die of natural causes, old age, etc.
He was not killed by lightning, or anything weather related.
He was not killed by an act of God (lightning, earthquake, forest fire, etc.)
There are no other objects of note anywhere in the field, and no objects have been removed or added since his death.
There are no tire tracks or other signs of another human being around him.
The man was not killed by any creature (snake, spider, etc.) that then moved (walked, slithered, flew) away.
The man did not kill himself.
This happened in the typical world, with regular laws of physics, a depressing lack of magic, and (sadly) no aliens.
After the first round of answers finding loopholes, a couple more notes. To those that this eliminates your answer, thank you for helping me find those loopholes:
The man's death was instant (no time for anything to leave the field before he died)
The man was not doing anything illegal.
The contents of the package did not cause his death.
There was nothing growing or living in, or recently added to the field that caused his death. The field is not toxic.