When is "Bismillah Al-Rahman Al-Rahim" said, and when is "Bismillah" said alone?

This issue is a matter of scholarly disagreement. The most complete form is to say "Bismillahir Rahmanir Rahim" (In the name of Allah, the Most Gracious, the Most Merciful) in all situations, but it is sufficient to say "Bismillah" (In the name of Allah). Some scholars are of the view that there are instances where only "Bismillah" has been mentioned, such as when entering the restroom, during intercourse, and when slaughtering an animal.