So this is how i think it happened

A Giant Shuriken was sailing at Hashirama after he as been tricked and Tobirama was like...

Tobirama: Hashirama dodge its a trick!!!

Hashirama: But Tobirama.......... trix are for kidsss :D

Tobirama: -facepalm- Oh boy Hashirama .... catch it.. catch it with your teeth.

Hashirama: Oh boy, oh boy oh boy Nii-san *Opens mouth and catches it*

Hashirama: See i did it... *paper bomb hisses then explodes* .... *dead*

Tobirama: Bro?