That grossed me out so much when I heard it.
According to a guy I met who had done a few videos, you have to stay hard for up to two hours.
During especially rushed productions we have the producer in the back room reviewing footage only a few minutes behind the live filming.
He went and color corrected the bloody mess to make it look like cum.
The only things that are illegal to film are children and animals, but besides that you can legally shoot what you want.
One of these times it was a moneyshot.