While I was reading through the Giant Toad's entry in the Monster Manual (p. 329), I found this passage a bit unclear:
Swallow. The toad makes a bite attack against a Medium or smaller target it is grappling. If the attack hits, the target is swallowed and [...] it takes 3d6 acid damage at the start of each of the toad's turns.
As far as I understand, this means that the acid damage will be dealt from the toad's next turn onward, as the current turn to swallow the target has already started and an action (Swallow) has already been made. It doesn't apply on the same turn as the swallowing.
Is my assumption correct?