Cannonball: Baron Munchausen voluntarily sits on the cannonball, accepting external truths or principles as self-evidently valid. He lets these truths propel him on a path, requiring no further justification.
Ducks: The ducks are a regressive chain, each duck pulling the next, and in turn the baron along ad infinitum, suggesting no ultimate grounding only an endless line of ducks.
Hair Pulling: Baron Munchausen attempts to lift himself by his own hair, representing circular reasoning.
These three images represent the Münchhausen trilemma.
There's also a bootstrap paradox, with events caused by themselves. E.g. going back in time to be your own parent.