>>82245414
You'd literally feel it and you'd see that there is no liquid, it's just a skin sack with two balls in it. The balls inside the sack move up and down depending on the temperature outside to ensure that semen survives, they couldn't do this if the sack was full of liquid. Here's a pic of balls from reddit for reference, notice that there is no liquid in the sack as the testicles are basically fully visible.