Who's tickling whom?
Yarwhal seems like a Marten creation more than Dora, and it would make logical sense for her to tickle him. What doesn't make sense is for Marten to shriek like a little schoolgirl caught in a volcanic eruption when tickled.
But it showed Marten's turn, so therefore it was Dora's turn next and SHE put down Yarwhal and argued it, and she's the one who shrieks (which makes a little more sense). But I can't picture Marten jumping on top of Dora to tickle her without Bad Things happening. Maybe he just gets ballsy when he drinks.