Imagine the first time the Senju kiddos realize Hashirama has a regegeneration ability?? After a moment of horror, Tobirama’s little science brain immediately latches onto that. Hey, what if I stabbed you in the heart, anija? If I cut off your foot, do you think it’ll grow back?

Butsuma, horrified:  You are NOT cutting off your brother’s foot!

Tobirama: But chichi-ue, it’s for science!

Butsuma, about to lose his mind, turning to his wife to please get her son under control, except he remembers that when they do stupid shit they’re his sons not hers, so there’s no point in trying. Great, so now he has to find something more interesting to distract Tobirama with… (Never mind that a part of him is also curious to find out if the foot would grow back or not. He’s an adult, he’s not going to experiment on his own son, nope.)