You've heard of Cartoon Physics, right?  Here's a partial list
of anime/manga Physics:

THE LAW OF SNEEZING:
(1)  If you talk about someone, that person will sneeze.
THE LAW OF FALLING:(Cf. GRAVITY LAW)
(2)  If the situation is serious and/or is building up to a climax,
    and you utter a nonsequitur or an anticlimatic phrase, then
    everyone else will fall down or keel over.
THE NOSEBLEED LAW:
(3)  If a male is suddenly stimulated by a female (especially an
    attractive one), then his nose will bleed.  In rare cases
    one nostril will bleed slowly; but in most cases, streams
    of blood will spurt forward from both nostrils.
THE MALLET LAW:(Cf. ANVIL LAW)
(4)  If a male does something that implies an attraction to another female,
    even for a brief moment, his intended female companion in the series
    may call into possession a great strength, sometimes manifesting
    itself in the form of a giant mallet.
THE FUNNY EPILOGUE LAW:
(5)  If a comedy series shows a serious episode, there is an 80% chance
    that a short (one-panel/30second) "epilogue" scene will be shown
    which contains some humor.
THE CAMEO LAW:
(6)  Any sufficiently long-run anime/manga will contain a reference to
    another anime/manga, sometimes unexpected.  (Ex:  Ranma 1/2 and Dr.Slump
    both contained references to Doraemon.  Where?)  (Doraemon itself
    contains references to Q-Taro.)
THE SECRET LAW:
(7)  If the protagonist has a secret and another character is introduced,
    then that character will either not discover the secret (despite
    obvious clues, usually) or become a supporting character in the series.
THE SPORT-HERO LAW:
(8)  If the protagonist is the best in some sport and a new challenger comes
    on the scene, then although the new challenger will seem to be unsurmount-
    able, the protagonist will defeat him in the end.  There is a 75% chance
    they will depart friends.
THE RUNNING GAG LAW:
(9)  Introductions have a 60% probability of becoming a running gag.
THE NONOMOHEY LAW:
(10) Extreme embarrassment, pain, or generic graffiti may be represented
    by the "no no mo he" face.
THE VOLTRON LAW:
(11) The transformation process into the "big" hero or machine is always shown
    in full but assumed to be done in zero time (as enemies apparently
    are frozen still).  This applies to many TV-serialized anime, but is
    seldomly done in manga.
THE CROW LAW:
(12) In situations with few people, a black crow flying overhead (uttering
    empty balloons) may be substituted for law (2).
THE DRAMATIC MOMENT LAW:
(13) The consistency of the background is inversely proportional to the
    degree of drama the moment applies.
THE DELAYED PUNCH LAW:
(14) The amount of time a punch makes contact is proportional to (a) the
    force of the punch; (b) the inverse of the seriousness of the situation;
    (c) the inverse of the number of previous punches in the scene.
THE PUPIL LAW:
(15) Pupil size changes with emotion and or seriousness.
THE HAIR LAW:
(16)  Hair color is relative, weird, or just relatively weird.
THE BEAD LAW:
(17)  In situations of extreme stress or exasperation, a large bead of
    sweat is allowed to coagulate on the character's head without 
    having to obey the laws of gravity and/or conventional physics.
    The bead of sweat can be much larger if the face is not seen.
FOLLOW-UP to (15)
Some pupil/emotion correlations:
(a)Single dot:  speechless surprize.
(b)NO hiragana: See THE NONOMOHEY LAW, above.
(c)Shojo eyes: Cuteness/Handsomeness (unless standard to manga)
(d)Large iris: Extreme emotion.  May be sadness or anger depending
    on shape of iris.