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*