Recent literature on non-human animal communication has unearthed call combinations that appear to follow internal rules of composition (e.g., Coye et al. 2015, 2016, Dutour et al., 2019, Suzuki et al., 2016, Suzuki and Matsumoto, 2022). Specifically, various studies have found a rudimentary, non-recursive operation that allows the combination of two atomic units; this is sometimes referred to as 1-Merge in a typology proposed by Rizzi (2016). Some of these combinatorial systems have been analyzed with tools from formal linguistics. These include call combinations found in Putty-nosed monkeys (Schlenker et al., 2016a), Titi monkeys (Berthet et al., 2019), as well as the –oo suffix in the alarm call system of Campbell’s monkeys, an early example initially discussed by Ouattara et al. (2009), and further investigated by Kuhn et al. (2014) and Schlenker et al. (2014). The –oo suffix can be optionally attached to the root alarm calls hok and krak, modifying the root’s meaning into that of a less urgent alarm.