There's really no biological undertone to all this, unless you count the somehow shapeless form of this rucksack as reminiscent of an amoeba. To be honest, I kind of do, which is the key appeal for me. It's become another appendage (sorry for the bio term excess), or bosom buddy (in more affectionate terms), that takes the meaning of 'cavernous' to another level. Stored in it: practically every life requisite thing. That, and all the necessities for cross-city trekking.
I've also gotten into the habit of hand-clutching- an insignificant note to make but I think it pertinent considering the nature of a rucksack. Emotions are setting in, I guess. 'Til death do us part.