ThingOne hasn't quite understood short sleeves vs long sleeves.
She thinks instead that she has short arms or long arms, depending on what top she's wearing. i.e. if she's wearing a long sleeved top she says she has short arms, and if she is wearing a short sleeved top she says she has long arms (as more of her arms are visible).
Makes some kind of sense, doesn't it.
The thing is, she genuinely believes she's more likely to be able to reach something if she's wearing a short sleeve top as her arms are longer. This leads to her taking the time to roll her sleeve up if she's wearing a long sleeved top and needs to reach something under the bed.
Great to see toddler logic at work.
(NB: I find this amusing to see every time she does it, which is quite often, so who's the real simpleton here?)