In Tanaka's office, Naoi vomits over his shirt. In the scenes after, his shirt is clean again.
Megumi get a lot more than two shots from a double-barreled shotgun.
When Naoi is vomiting, it appears to be coming out even though his mouth is not fully open.
The "anus" from which the tapeworms are seen emerging are clearly too high up on the actors' backsides (being roughly where the tailbone is).