The blood radical and blood are the same in looks as well as in meaning.
To remember the reading けつ, we use the word "ketsup." The perfect mix of ketchup and catsup!
The radical is technically blood, but you know that radical is just a drop (of blood) on a plate. So, you ask yourself... Is that really blood on the plate? Could it be? You decide to take a gamble and lick it off. When you taste it, it's definitely not blood. No, it's ketsup (けつ).