There is an abandoned aquarium in an empty house. The aquarium has three large fish and three small fish. But after a week, one large fish and two small fish die.
I’m in an elevator with two other people. When it reaches the first floor, one person gets out and six get in. When it reaches the second floor, three people get out and twelve get in. At the third floor, five leave and nine enter. It rises to the fourth floor, one person gets on and the doors close. Suddenly, the elevator cable snaps and the car smashes to the ground. No one survives the fall, yet I’m alive and know exactly how many people go on and off the elevator at every floor. How is this possible?
Alcohol. People have a drink to celebrate, but also drink to hide their shame. Lastly, drunk driving is a crime.
A mask is also a valid answer. They can be used to celebrate Halloween or at dress-up parties, a mask can hide your shame and masks are used by thieves.
Update: This one has more valid answers than I thought. Money, drugs and night also work.
Lucrezia Borgia invited a prospective victim to lunch. They ate a hearty meal of roast venison, with a selection of fresh vegetables, all washed down with the finest wine imported from Bordeaux, France.
After the meal, they ate figs and freshly picked grapes.
“Just one apple left”, said Lucrezia, “I insist you have it.
“No”, said the guest, “I couldn’t”.
“Tell you what”, said Lucrezia, “we’ll share it”, and promptly sliced the apple in two with her sharpest knife. The guest and Lucrezia started to eat their respective halves when the guest’s eyes rolled towards the ceiling and he fell over, dead.
“Another victim successfully dispatched,” thought Lucrezia.
Nipples or teats. Cows have four of them, dogs usually have eight and a human (assuming that’s who’s reading this) has two. Cows milk standing up, dogs often lie down and women usually sit when breastfeeding.
A tailor can make a pair of pants from the scraps left over from sewing up five pairs of pants. If he has twenty-five scraps, how many pairs of pants can he make?
Six pairs of pants. He can make five initially, but once he’s done making five pairs of pants, he’ll have five remaining sets of scraps, meaning he can make an additional pair of pants, totaling six.