Director Fran Agulló declined to direct his next short film 'H&H' and gave Marco Huertas the chance to direct it. While developing the project under the title 'El amor y la violencia (The love & the violence)' he felt uncomfortable, as if he was ''having sex with a mate's ex-girlfriend''. He convinced Fran Agulló to re-approach the project to direct it under his original vision and decided to work on 'Las Bestias (The Beasts)' instead.
'Las Bestias (The Beasts)' is an adaptation of an original screenplay by director Marco Huertas called 'The Tiger'. The early screenplay was too complex to produce and the makers found out it had several similarities with an upcoming Darren Aronofsky project with the same title. The screenplay was changed inspired by actual events that actually happened in Zannesville, Ohio (USA) in 2012. While 'The Tiger' events happened in 1910's East Siberia, the story was translated to nowadays Barcelona (Spain).
Abdelatif Hwidar was cast as Koke, but had to drop out days prior to start shooting.
Ramón Orozco was cast as Sami but had to drop out due to scheduling conflicts the week prior to start shooting.
After Abdelatif Hwidar left the project, the role was then offered to Jan Cornet, Víctor Palmero and Tony Corvillo. Borja González-Ayllón was very willing to step into the role. Abdelatif Hwidar himself dealt with his agents to help the filmmakers find a proper substitute for him. Sebastián Montecino was then cast.