Day of the Dead, itself preceded by Creepshow. I imagine most Romero fans at the time (and even today, possibly) anticipated another splatter piece in a similar vein as those two titles.
But that's not what audiences can expect from Monkey Shines. Not only is this the first true studio film for the notoriously independent Romero, Monkey Shines finds him staking out a more restrained and (comparatively) mainstream thriller instead of an ultra-graphic, comic-book apocalypse. It's not without its flaws, but it's a welcome change of pace from the undead master, and it finds him once again exploring a familiar theme: man's darker instincts and how they manifest themselves.
Allan Mann (Jason Beghe) has it all: a great physique, a beautiful girlfriend (Janine Turner), and is a standout track star and law student. One morning while out for a jog, he's struck by a truck and left paralyzed from the neck down. His girlfriend leaves him for the surgeon (Stanley Tucci) who operated on him, and his overbearing mother (Joyce Van Patten) hires a shrill nurse (Christine Forrest) who belittles and insults him. Depressed, Allan attempts suicide but fails. To help him out and cheer him up, his best friend Geoffrey (John Pankow) gives him a helping hands Capuchin monkey Ella (Boo with vocal effects by Frank "Megatron" Welker). Immediately, there's a connection between man and monkey; Ella seems to anticipate his every need and want, and Allan's spirits lift. What he doesn't know is that Geoffrey, an amphetamine user and chemist, has been injecting Ella with a compound composed of human brain cells to make her smarter, and Ella reacts jealously when Allan falls for animal trainer Melanie (Kate McNeil).
The violence is nowhere near as extreme nor as graphic as one would expect from a Romero movie (longtime collaborator Tom Savini is credited with the special makeup effects but doesn't get to do much). Much of its suggested, occurs off-screen, or is relatively bloodless. The tension comes from Allan's vulnerability; trapped in his useless body, he's no match for the nurse's pet bird, falling off the bed, or a four-pound simian that can scamper across furniture or hide under the bed, springing out when least expected. There's also the rage that overtakes his personality. The fact is Ella wouldn't do what she does unless there was already something bad inside of Allan for her to feed on. Man(n) has created a monster acting on instinct that he cannot control.
The other villain of Monkey Shines is science run amok. Even after being told by Allan something weird is going on with Ella and witnessing her behavior, Geoffrey continues to inject Ella with more of the serum to make her ever smarter. Why? A professional rivalry with the dean of his university (Stephen Root). Geoffrey believes his experiments are going to "strike gold," as he puts it, so he allows his friend to be exposed to a potentially dangerous animal. Human anger, jealousy, vanity, greed, and neglect are the perfect potion for creating a monster.
Also, an otherwise effective climax involving a battle wits and wills between Allan and Ella is undercut by its resolution in which Allan suddenly finds the strength to move his hand at the right moment. Also lame are the "Carrie"-type ending (you know, one last jump scare, but it's ok because it's a dream) and the schmaltzy denouement.
Romero has always demonstrated his value as a director by going beyond the surface shocks, and that talent is on display in Monkey Shines. Yes, there is a shrieking, howling monkey chasing people with a razor blade and syringe by the end, but the deeper psychological horror stems from the human evil: the irresponsible scientific experimentation that created the monster and the repressed anger that fed her.