Hi Carlos: The pronunciation of your grandpa's can be transcripted as /mokreysh/, stressed on the first syllable. The word sounds like the name of an animal because of its ending, but there isn't actually an animal of this name. The name is derived from the adjective "mokrý", which means 'wet'. As a family name, it not uncommon. You can find some Czech sportmen with this surname on the Web. Jirka
There are more similar family names in Czech: Mokrý Mokroš Mokrejš All of them are with high probability derived from the adjective "mokrý" = wet. The translation could be "Wetman". Poronounce it as "mock" and "rate" together, but with "sh" instead of "te" in "rate" :wink: