There are some sound changes which happen in fast or casual speech in Dothraki. For instance, the preposition ma, and all prepositions that end with a vowel, often ellides to an m' in front of words that begin with a vowel. Mr'anha is an example, where mra and anha have ellided together.
Other sound changes often occur. For instance, fonashek is an ellided form of fonas check, meaning hunt well.