The article is an English-Serbian contrastive analysis of the patterns of idiom variation resulting from the processes of formal and semantic decomposition and re-composition. The research is grounded in the assumptions of Conceptual Metaphor Theory, Mental Spaces Theory, and Conceptual Integration Theory, which provide the background for the analysis of formal and semantic flexibility, as well as literal and figurative meaning interpretation behind the processes of decomposition and re-composition. The empirical analysis includes 22 common English and Serbian animal idioms and more than 200 idiom variations. The results show five patterns of variation. The three most dominant types are lexical substitution, vehicle replacement, and structural expansion in both English and Serbian, suggesting underlying similarities in meaning interpretation based on our shared cognitive system. Another finding shows that a variation pattern can be language-specific, for example, key lexeme repetition in English, indicating that cross-linguistic and cross-cultural specificities should also be considered.