The Head-to-Toe Guide to Guys.(physiological facts)

Men don't come with instruction manuals, but life would be a lot less confusing if they did. Well, you're in luck. Herein lies all the info you need to better understand the male machine-and get maximum user satisfaction.

* Think you have your Y-chromosome counterpart almost figured out? Don't be so sure. There is still a ton of hombre information you haven't heard about--until now. To help you out, Cosmo has collected a wealth of little--known facts on men's erogenous zones, sensual preferences, and hard-to-tame tendencies, then crafted them into a handy allover guide. Armed with this newfound knowledge and our advice on how to use it, your guy IQ is guaranteed to jump to genius.

1 TUNNEL-VISION TEASER

Men can see farther than women can, thanks to their caveman ancestors who were hunters and had to spot prey from far away. However, they have a much narrower visual field than females do, according to Why Men Don't Listen and. Women Can't Read Maps by Barbara and Allan Pease. So before you read your guy the riot act for blatantly ogling another girl, read this: Sex researchers report that women look at men's bodies as much as--and sometimes more than--men look at us, yet we ladies rarely get caught because of our incredible peripheral vision (nearly 180 degrees)!

2 EYE-CANDY CLUE

The quickest way to turn on a man is through his peepers. Men--as opposed to women, who generally require such sensory stimuli as the touch of a hand or a seductive whisper--can become fully aroused just by looking at an attractive image, say Anne Moir, Ph.D., and David Jessel in their book Brain Sex. This explains why so many guys prefer making love with the lights on. It's also why they have more of a jones for porn than women do.

3. PERK-UP-HIS EARS-TIP