I do this on Les Pauls with humbuckers. Whether or not it works with other guitars will depend on the setup. Just press one of the unwound strings down hard between the end of the fretboard and the neck pickup. The string initially contacts the back edge of the pickup, then tilts the pickup until the string hits the forward edge. Voila -- you've got a seagull squawking. The E, B and G strings each do it at a different pitch. With a delay/repeat it sounds like (sorry) a flock of seagulls. Also, try with a wah for variation. Note: it will scratch your pickup covers, so if you're a dead mint freak, don't bother.