Does the Giant Toad's Swallow acid damage take effect only at the start of its next turn?

Question

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?

Answer 1

Your interpretation is correct

As you noted, Swallow is an action that the Giant Toad takes, usually during its turn. Since the acid damage is dealt "at the start of each of the toad's turns" this means that it will only happen at the start of the toad's next turn and not during the turn in which the Giant Toad used Swallow, as you correctly deduced.

As a small note for completeness, if the Toad for some reason is able to use Swallow outside its turn, for example by using the Ready action, the damage will be dealt the next time the toad gets a turn.

Answer 2

You are correct

The frog's turn starts (no swallowed creature so no acid damage), then during its turn is swallows a creature. Then, during the next round, it has a turn, that turn starts and the swallowed creature takes acid damage.

Answer 3

Correct

Effects do exactly what they say they do. There are several other creatures, such as the Remorhaz that have similar abilities. The damage being dealt only at the start of the turn is offset by the fact that the creature is only swallowed if the attack part of the Swallow action is successful. In that case the creature takes damage from the attack on that turn, is swallowed, then takes damage at the start of each turn from then on.