One song–"Bidi Bidi Bom Bom"–was improvised during a rehearsal starting off as a song with few, if any, lyrics. The band's drummer, Selena's sister Suzette Quintanilla, said "we were goofing off" and insisted that after A.B. began playing a groove on his guitar, Selena started singing, coming up with lyrics "as ideas came to her." It started off with lyrics about a cheerful fish swimming freely in the ocean, which Astudillo likened to a nursery rhyme, organized around a wah-wah guitar riff using a crybaby that was improvised by Pérez. The track, then called "Itty Bitty Bubbles", became an extended jam during the band's concerts to prevent promoters from reducing their pay for playing for a shorter time than promised. Selena performed the song at the La Feria concert in Nuevo Leon in September 1993, a day before the singer and Astudillo began "the lyrics and melody together". A.B. saw potential in the tune and "nipped and tucked what Selena [had already done". He joined as co-writer, writing the guitar solos for Pérez, as well as the arrangements for the song. A.B. called it "kinda a little scary" finding the project the first of its kind. The day before the band was scheduled to record the album, A.B. approached Pérez and asked if he would be interested in working with Vela on "Ya No", a song that A.B. had written. Pérez worked with Vela throughout the night improvising the drum sounds and programming the music for it, adding electric guitar riffs, and complementing it with his own musical style. Pérez was dumbfounded that despite A.B.'s assistance he had been given creative control over the track.