Apply DJ-style scratching over music and annoy girlfriends, free of charge.

What do Katy Perry and Lindsay Lohan have in common? If you said “not enough wiki-wiki sound effects in their music,” then two things: 1) Thanks for not paying attention to girl/girl kissing hype and 2) MixMeister Scratch is the free app for you.

While MixMeister makes very powerful professional DJ software, Scratch does just one thing; it lets you layer vinyl-scratching sounds over any song in your music library. Just start a song from the iPod interface, return Home, and then launch Scratch. The app opens to a menu of 10 built-in audio files, including beats, spoken phrases and sound effects such as Laser, Scribble and Air Raid Siren. Choose one, and it begins playing in a loop. On the turntable-inspired main screen, you slide your finger across the record to emulate a DJ scratching vinyl. Response to finger movement isn’t exactly real-time, but you can work some furiously fast scratches, slow, dragging scratches or finger-tapped stutter playback. The sound is also realistic, which is the best part. There’s also a start/stop button for Scratch’s loops, and a volume fader for adjusting the loop relative to your chosen song.

Don’t expect to have your mind blown, but all it costs is 3.2 MB of your device’s memory.