lundysd:I'm a DM candidate right now, and a fellow candidate (who shall remain nameless but was certainly crucified) was asked to perform a demonstration of a feet-first snorkel dive. Everything was quite exemplary, except for the lack of a snorkel in said DM's mouth (disclaimer: I did a pretty darn lousy pike dive myself, so I am in no way judging)
Actually most well trained freedivers remove their snorkels, make a dive, then replace it after many breaths at the surface.
Chad