Animal minds are simple, and therefore sharp. Animals never spend time dividing experience into little bits and speculating about all the bits they've missed. The whole panoply of the universe has been neatly expressed to them as things to (a) mate with, (b) eat, (c) run away from, and (d) rocks. This frees the mind from unnecessary thoughts and gives it a cutting edge where it matters. Your normal animal, in fact, never tries to walk and chew gum at the same time.
The average human, on the other hand, thinks about all sorts of things around the clock, on all sorts of levels, with interruptions from dozens of biological calendars and timepieces. There's thoughts about to be said, and private thoughts, and real thoughts, and thoughts about thoughts, and a whole gamut of subconscious thoughts. To a telepath the human head is a din. It is a railway terminus with all the Tannoys talking at once. It is a complete FM waveband - and some of those stations aren't reputable, they're outlawed pirates on forbidden seas who play late-night records with limbic lyrics.
Terry Pratchett, Equal Rites (1987)