When doing a FIND search (Command + F) for jpegs by key words in a file title, FIND sees "jpg", but not the words in the title preceding ".jpg".

I.E., I want to find a jpeg file named "Cat.jpg". If I type in "jpg", FIND will locate all jpegs in a folder or on the computer. BUT if I type in "cat" it sees nothing. This is weird..... Why is this? FIND seems to see all words in other types of files and folders.