I'll start this post by saying (and hopefully heading off the snide remarks! ), that, yes, I know that Serbian != Russian. They are two distinct languages. With that disclaimer out of the way...
I was watching a film a few days ago, and the Serbian villain, speaking that language, told one of his henchmen to essentially "think!" or "use your head!" (they were talking about some evil plans or something). He used a word that sounded like Мышай! which, to me, sounds like an imperative verb form of the Russian word мысль (thought). Does a similar verb form exist in Russian?