Fill a cocktail shaker with ice. Pour in the tequila, Cointreau, blue curaçao, and sweet and sour. Shake vigorously for 30 seconds.
Place margarita salt on a small plate in a thick layer. Cut a slit in the center of the lime wedge and then place it on the rim of your glass. Run the lime wedge around the entire glass to get the rim wet. Remove the lime wedge and dip the rim into the margarita salt.
Fill the glass with ice, being careful not to knock the salt off the rim.
Remove the lid of the shaker, and strain the margarita into the glass.
Place one test tube inside one shark until it is all the way in. The test tube will stick out a little bit. Fill the test tube with grenadine until you can just see the grenadine above the shark's mouth.
When you're ready to serve, quickly turn the shark over into the margarita and plunge the test tube (and shark's head) into the margarita so the grenadine slowly bleeds out into the cocktail.