The Star Mouse by Fredric Brown

To say it was a strange experience for Mitkey is understatement. Knowledge is a strange thing, even when it is acquired gradually. To have it thrust upon one --

And there were little things that had to be straightened out. Like the matter of vocal chords. His weren't adapted to the language he now found he knew. Bemj fixed that; you would hardly call it an operation because Mitkey -- even with his new awareness -- didn't know what was going on, and he was wide awake at the time. And they didn't explain to Mitkey about the J-dimension with which one can get at the inwardness of things without penetrating the outside.