How to Find two words in the middle of the SUBJECT?

I need to search for messages with two or three workds that will appear together, but in any position in a subject like.
Example:
The Dog is Big
and I need to find 'Dog is'
What is the correct REGX for this?
Thanks
Example:
The Dog is Big
and I need to find 'Dog is'
What is the correct REGX for this?
Thanks