What’s good about the toilet is the flush completely rinses the shampoo clean.
_supposedly_ the cold rinse is better because it closes the pore that the warm wash water opened up. Supposedly also true with ‘sealing the hair’ in some way.
I suppose there’s some truth to it. Hair’s mostly what, silicon? And silicon reacts to cold by its molecules coming closer together, and silicon which has closer together molecules will give your hair a nice sheen.
So, might be true enough. Then again, I could be completely and utterly wrong.