When playing HoN I often deny ally's when they are have Dots (Damage over time) on them. As an example you can deny if a hero got little HP and have Slithers "Q"-Spell on them...
But yesterday i played and i couldn't deny an ally that had Blood Hunters Ulti on him.(less then 10% HP when i tried to deny). So that made me wounder.
Which attacks/dots from enemy heroes makes it possible to deny allied heroes?
EDIT: Still the question remains which spells counts as a dot, is there something that distinguishes regular spells and dots.(Something that would be visible, or is this more of a "general knowledge" question)