Circus is a rethemed Breakout where you control a seesaw in order to help two clowns (or stick figures if you don't believe the game's marketing) to amaze the audience by jumping high and popping all the floating balloons, forever and nonstop. People will lose legs during this show indeed.
There's an extra, unused frame for when the clowns fall on the ground.
Present at 1510 in memory:
The game never actually prompts for a coin to be inserted. Instead, the "CREDITS" amount appears if coins have been deposited and the game is ready to be started.
Present at 1590 in memory:
This could have indicated the bonus credits gained by the player as it is with the bonus points, but it's not used anywhere.