It turns out that there's a funny reason why Arya knew to look in the mattress for that letter in this week's Game of Thrones.
'Eastwatch' saw Littlefinger try to play the Stark sisters against each other as he made the point of 'hiding' the letter that Sansa (Sophie Turner) was coerced by Cersei to write way back in the first season.
Arya (Maisie Williams) spotted it and broke into Littlefinger's room to find what he'd hidden, looking in conventional places before finding the letter in a slot in the mattress.
Odd, no? Well it turns out that there's a bit of family history when it comes to why Arya decided to look in the mattress, and we were told about it back in season three in a conversation between Sansa and Tyrion.
After he was laughed at by Lord Desmond Crakehall, Sansa told Tyrion that he should stuff the Lord's mattress with sheep shit to get back at him as "his room would stink, but he won't know where it's coming from".
Sansa tells Tyrion that she got the idea from Arya who used to do it to her "when she was angry with me", so no wonder she thought that the mattress might be the best hiding place.
Especially because you could assume that Littlefinger might be staying in Sansa's old room in Winterfell, given that she's moved into her parents' room, so the slot in the bed would already be there.
Of course, Arya doesn't yet know that she wasn't being clever, Littlefinger definitely wanted her to find it…
