In this talk I will review evidence from several studies using event-related brain potentials and eye tracking to illustrate the formidable complexity of language interactivity and cross-linguistic effects in the bilingual mind. For instance, I will show how bilingual adults spontaneously and unconsciously access the native translation of second language words (Thierry & Wu, 2007; Wu et al., 2013) and they unknowingly stop accessing these representations when second language words are unpleasant (Wu & Thierry, 2012). Even more surprising, bilinguals appears to speak two languages at once, although we can only hear one, that is, they unconsciously access the sound of words in their native language while speaking in their second (Spalek et al., 2014). More surprising even, cross-language effects extend to the domain of syntax: Welsh-English bilinguals spontaneously apply the word order of Welsh in an all-in-English context (Sanoudaki & Thierry, 2015) and they transfer to English a morpho-phonological transformation rule of Welsh that is entirely alien to English (Vaughan-Evans et al., 2014). In closing, I will present some recent data showing how language of operation can shift cultural expectations whilst expectations derived from generic world knowledge are unaffected. Taken together these findings reveal unsuspected levels of cognitive diversity linked to language variations within and between individuals. We can only understand the nature of our mind in a conscious fashion, yet a great part of what defines us and our understanding of the world comes from language. This realization calls for a reconsideration of the way in which we conceptualise cognitive operations classically considered to be ‘under our control’.