Some athletes that want a physical edge, but not a lot of extra mass, have begun experimenting with growth hormones from animals that are smaller than human. Mouse and marmoset growth hormones are the most popular so far. Their effect on the human body is still uncertain, but there are some shortstops who swear that the marmoset hormones have made them more alert and able to catch very hard hit balls. On the downside, they have become extremely paranoid and have started jumping to safety at any unexpected noise.