Bomba is the Afro-Puerto Rican drum-and-dance tradition of the coastal sugar towns (Loíza, Santurce, Ponce, Mayagüez); sicá is its most widely played rhythm. The dancer challenges the lead drum (primo or subidor), which answers every move — so the groove underneath has to be rock-steady.
How it sits: no clave. The timeline is the cuá, two sticks on the side of a drum or a wooden tube (rim), which plays the cinquillo every bar. The buleador — the low barrel drum (conga-lo) — repeats a two-bar ostinato: a bass stroke on 1, an accented open tone on the and-of-2 with another on 3, and a pickup on the and-of-4 (bar 2 adds a tone on 4). The singer's maraca (shaker) runs even eighths. The primo is left out: it improvises.
Listen for the cuá and buleador agreeing on the and-of-2 — that shared stroke is the heartbeat of sicá.
Practice: clap the cuá while saying the buleador's open tones aloud.