"I have learned the difference between a cactus and a caucus. On a cactus, the pricks are on the outside"

Mo Udall’s remark cleverly contrasts the literal characteristics of a cactus with the figurative qualities of a caucus, the formal gathering or meeting, especially in political contexts. The humor lies in playing on the double meaning of the word "prick", which refers both to the physical spines that cover cacti and to an insulting slang for unpleasant or disagreeable people. In the natural world, a cactus is easily recognizable because its sharp spines are visible, warning you to handle it cautiously. Its dangers are external and apparent to anyone who approaches.

By comparison, a caucus, often a political meeting or assembly meant to coordinate strategies and make decisions, is populated by people whose capacity for difficult or abrasive behavior may be hidden beneath a veneer of civility and decorum. In such environments, individuals who undermine, betray, or belittle others might not reveal their antagonism outright. The observation is that, unlike the cactus, whose threat is outward and obvious, the "pricks" in a caucus present themselves in more subtle, internalized forms. This critique points to the often duplicitous, sometimes ruthless, nature of political gatherings: one may enter them thinking all participants are united by common purpose, only to discover rivals, opponents, or saboteurs disguised as colleagues.

Udall’s quip encapsulates a broader skepticism about political culture, suggesting that hurtful personalities or underhanded tactics are a hidden danger within apparently cooperative groups. It also speaks to experience, one must endure enough time among either cacti or caucuses to know where the true risks reside. The line works as biting social commentary, mocking the lack of transparency and trustworthiness in some political environments while offering an amusing metaphor: at least a cactus is honest about where its barbs lie. For those navigating power structures, the lesson is to be vigilant for hidden threats in the most genteel spaces.