"Voor de muis is kaas de enige motivatie."
Translation:For the mouse, cheese is the only motivation.
Why is the 'is' after mouse, is it because it part of the second clause and brought to the front of it
It's because the sentence began with something other than the subject (in this case, a prepositional phrase) and as Dutch is a V2 language, the verb must be the second element in a main clause. So, the verb and the subject are inverted.
Note that one could say:
Kaas is de einige motivatie voor de muis.
In that case the prepositional phrase (voor de muis) has been moved to the end of the sentence.
Hope this helps.