Thanks PP! As for the question, I have idly wondered that myself from time to time. It is a surprisingly large subject. For a start I am pretty sure that there are different classes of reaction, ranging from letting go all the irrelevant muscles when it is a life-or-death matter, and any repellant effect on the predator being adventitious, to certain creatures, such as some snakes, having decidedly nauseating excreta that they systematically smear on anything holding onto them. In this their behaviour resembles that of skunks and some insects such as stink bugs, that let go with special glands that have nothing to do with their excretory systems.

However, there also are some of our nervous systems that control  our entrails' tone and control under strees or if we get killed. Their effect is incidental I suppose. It might actually be attractive to some predators.

Then again there is the matter of social interaction. A puppy will roll over and urinate in submission, and there are other examples of such mammalian physiological semiotics as well.

It also might repel attackers that find such materials distasteful, unlike  predators that presumably regard guts mainly as condiments.

But all such things are largely handwaving and speculation. If you have any ideas, feel welcome to air them.