A variant of the
blown raspberry: Place your lips firmly on the
belly of the recipient, and blow to produce a
ribald noise. This is perhaps the easiest way to make a baby laugh.
The romantic belly raspberry must be done carefully. In an intimate moment, gently kiss the belly, then perform the raspberry. This is a tremendous tension breaker, and has the advantage of relaxing the recipient. Warning, though, some people are turned off by all forms of raspberries. To minimize damages, try to keep the raspberry short and moderately dry if this is a first time with a partner. The sensation produced isn't enormously erotic, but rather tickles pleasantly.
Never perform this manoeuvre on a woman in a bathing suit unless you have discussed it beforehand.
The pet belly raspberry should not be performed in public. However, there is no shame in secretly raspberrying a dog or rodent pet. Do not attempt on a cat, or a hamster, and especially not on birds. Most animals that enjoy a belly rub will enjoy the belly raspberry. (Pet rats really enjoy this.)
The comedy raspberry requires misdirection: pretend to be concerned about something on the surface of the belly (ie: "Hey, is that a papercut?") and go in for closer inspection. It is best to create an air of concern, as this creates an increase in tension, which increases the comic relief. Even if the recipient is a baby lacking comprehension of the situation, employ misdirection. (ie: "Oh oh, what happened to your belly button?")