"The mouse is eating bread."
Translation:Мышь ест хлеб.
Russian word order is based on 2 main rules:
- the new information generally comes at the end of the sentence,
- there is a default word order for some words (and if an object is expressed by a noun or by a phrase, its default place is after a verb; if it's a pronoun, it usually comes before the verb), and moving the word from its usual place makes the word emphasised.
Here, you've swapped «ест» and «хлеб», and put «ест» is the end, to make it emphasised as the most importain information.
So, «Мышь хлеб ест» emphasises «ест», it makes it the most important thing you want to say. I.e. the listener knows there's a mouse, the listener knows mouse does something with a bread, and the new information is that it eats it (and doesn't carry it).
You could imagine some contexts where «Мышь хлеб есть» would sound OK (for example, as an answer to the question «Что мышь де́лает с хле́бом?» 'What does the mouse do with the bread?'), but in most cases «Мышь ест хлеб» sounds much better.