In Kill Bill Vol. 2, Elle Driver plants a black mamba in the case of money that she brings to Budd when she purchases Beatrix's Hanzo sword from him.
Earlier, Bill and Budd have a conversation about the Hatori Hanzo sword that we later discover was a gift to Budd from Bill.
BILL: You haven't by any chance kept up with your...swordplay?
BUDD: I, uhm...I pawned that years ago.
BILL: You hocked a Hattori Hanzo sword?
BILL: It was priceless.
Bill appears to be annoyed with Budd when he discovers this. Bill continues to speak with Budd about the past and to not be angry with him anymore.
After Budd gets bitten by the black mamba and is lying on the floor dying, Bill calls Elle while she is putting the money back into the case.
Bill...I have some tragic news. Your brother's dead. I am so sorry, baby. She put a black mamba in his camper. Look... I can be there in about 4 hours. Do you want me to come over? No, no, no, no. You need me, baby, I'm there.
It just seems like a coincidence that Bill would be calling Elle right at this time. Did Bill know that Elle was going to kill Budd? Since Bill was annoyed with Budd due to Budd hocking his Hanzo sword, did Bill set this up somehow behind the scenes unbeknownst to Elle?