One of the definitions of logic is that it holds water for everyone. Whether you live in County Kildare, walk on the moon or are a dolphin.
But is that so self-evident? A famous example is the Raleigh ad. You see an African on a bike who is chased by a lion. The message was that on this bike you were too fast for a lion. But the Africans saw that very differently: that cycle attracted lions.
The logic attributed to humans and to animals can be poles apart.
If we, humans, want to transport something we usually start by picking it up. Logical, isn't it? Gravity pulls it down so we counteract it. But if Dusty wants to transport a bunch of seaweed, like in the video, lifting it does not work as this weed floats. Therefore she pushes it down in order to 'hold it' and bring it closer. In Dolphin Address nr.8, 2002 I noted what solution she had found to push a waterwing without it getting washed over her. Then she also turned on her back, 'caught' the floating wing in the notch between beak and forehead and swam away with it. At that time I thought she had specifically invented this. Since then I have seen her moving objects in a similar way more often. I think this approach is part of a daily routine, an intuitive 'problem solving', like when we are lifting things.
The same continuous, but to the naked eye invisible, routine Dusty applies to her volume control. At that time the eye opener, that she can increase her buoyancy by expanding her chest, was a profound think tank thing.
A bit of a swimmer knows that at the surface you float higher with filled than with empty lungs. The weight of air is negligible. Essential is the increase in water displacement.
Oddly, though, I do not seem to decrease my buoyancy by pulling in my tummy. Might this be Archimedes' heel?
Unfortunately we cannot draw breath under water. But we can expand our volume with a diver’s outfit, in particular with a stab(bilisation) jack. This is an inflatable jacket that enables you to control your water displacement in order to neutralise your weight at any chosen depth. This does take some practice. If you let too much air (from your diving bottle) go into your stab jack you'll go up. The surrounding water pressure then decreases, therefore the air in your stab jack expands, your water displacement increases further, therefore you ascend further (and faster) etc. Divers call this 'a balloon ascent'. This you can counteract by timely deflating your stab jack, but not too much, as then again you will sink. To Dusty Archimedes' principle applies as well. But her volume control is fully integrated.
As volume increases disproportionally faster than pressure decreases, the closer to the surface the stronger the buoyancy force. And as the dolphin depends on the surface for breathing, this mode of transport is also at her disposal.
The closest I come to sensing the diminishing of water pressure is when I am about to surface after a snorkel dive. Though I always do keep a bit of spare breath, I usually rather long for air. So for me it is quite critical that I know precisely when I can breathe again. Only then I push out my last bit of air in order to empty my snorkel and then breathe in immediately. If I do this too early, I get water in when I'm in very need of air.
In the course of lifelong snorkelling I can feel by the pressure around my head when the entrance of my snorkel comes within reach of air. Dusty must have a much more refined sensitivity, not only for knowing when she can breathe, but also to adjust her body volume to the depth at which she swims or where she wants to go. The closer to the surface, the more acute this gets.
If you want to understand the world through the eyes of a dolphin, you should at least become aware of senses and sensitivities that you do not have yourself. By getting conscious of these intuitive instruments you also get insight in their logic cycles. And those do not always track with ours.