Well to sum it up, me and a buddy were on our second shore dive of the day. A nice 92 degree sweltering heat with not too much of a breeze and a 200 yard walk from the black asphalt parking lot to the water. Keep in mind, we did this once already. On the 200 yard surface swim, I stayed facedown with snorkel breathing and was just enjoying the cool(87degrees) water here in Pompano Beach, FL. I was by no means too tired to dive but a little on the lazy side by this point. At our descent point my buddy looked at me and gave me the, "let's go down signal". I signal back, "OK", and he submerges first. I submerge next and about 3 feet down I realize my regulator is not in my mouth, but my snorkel is! I found out the hard way by taking a small gulp of seawater. I immediately spit out my snorkel with the seawater and that is where some training dives paid off. I just calmly did an arm sweep, found my reg, purged the reg in my mouth and started breathing. Close enough for me! So now my routine includes hearing the air flow out of my reg at the surface before I try to dive. This is a redundant check for an 'on' tank valve and not trying to breathe with a snorkel underwater.