by robertg611
One point I found that may support the OPs interpretation is the Turn Order shown on the fourth page of the rules:1. If you are knocked over, stand your figure back up on its space.
If you are on more than one space, choose one of them. If you
are not on any spaces, see Odd Starting Spaces below.
2. Play an action card from your hand. You must move the full
amount shown. You may do its action.
3. Draw a new action card.
4. Reset the island. Return all marbles to their preset spots.
Ember marbles go onto the summit, and fireballs go into the
Scar. Reset any bridges or the ladder if they were disrupted.
He's placed in the cave during step 1 but you don't do any actual movement until step 2. (However, I don't have any of the expansions so I don't know if there are any additions/modifications that change this sequence.) If he's Snared during step 1, does he still have to play an action card from his hand during step 2 to no effect? Does he still draw a new action card in step 3 if he doesn't play a card?
There's a possibility that the Snare card could be played during step 2 as he's leaving the space but that definitely goes against the wording on the card that specifies entering the space.
I'm pretty sure the OP is correct that the card couldn't be played but I would assume that expansion that adds these take-that interrupts would have something to say about the timing of these cards.