That's sorta the point: it's trying to express the insanity (and inanity) of war and how, if viewed slightly askance, how ridiculous we are as a species. It does this by a sort of comic-surreal-incoherence (before getting quite dark near the end).
The book jumps around all over the place as well.
I've always thought this was a great film and does a near-impossible job of filming a nearly quite unfilmable book. Alan Arkin is superb in this (as he is in Wait Until Dark: i've always thought he was a very underrated actor).