Wow! It's so simple but is quite fun! Thank you for sharing this creation. May I offer for your consideration some ideas to enhance the game:
Add text at the beginning that says "Click the bull (red square) to begin and hang on for dear life!"
Have a timer showing the number of seconds you've stayed on the bull.
Maybe a cow sound effect once the player clicks on the bull to start the game, and a subtle rumbling sound after the game starts.
You can take these suggestions or leave them. Totally up to you!