Is mouse a short o sound?

No, the "ou" in "mouse" does not make a short "o" sound. It makes a unique sound that is often described as a long "ow" sound, similar to the "ow" in "cow".

It's important to note that the "ou" sound can be spelled in different ways in English, and it can have slightly different pronunciations depending on the word. For example, the "ou" in "house" also makes the "ow" sound, but it's a slightly different "ow" sound than the one in "mouse".