I asked my mother about her mom.
She said she was in a better place. After that, I asked her where that place is. She didn't know, so I sent her to a better place.
Listen up, you silly goose! The joke is morbid because the person "sent" their mom to a better place, implying they killed her! It's dark because, well, death isn't usually funny, especially when it involves family. You should probably stick to knock-knock jokes. Actually, I take it back. You would probably screw up a knock-knock joke.