Q: How do you keep an elephant from charging?
A: Take away its credit cards!
Explanation: When an elephant runs towards you or something else, we say the elephant is charging, much like a bull might charge (run) at the cape of a matador. To charge is also to pay for something by credit card. The beginning of the joke makes us think of how to stop an elephant from running at something- very difficult to do!
This joke is funny because it plays with the two of the meanings of the word charge: a way of moving forward and using a credit card.
The word charge has many other meanings, such as charging your phone or to accuse someone of doing something wrong.
Here is an elephant charging and someone stopping it: