context: A very brief pre-credits sequence shows an execution beside a pool, where a young blindfolded woman is decapitated by a man while two other complicit individuals watch.At a university, Dr. Ernst Prell (Alan Brock) lectures a small group of four students, Keith (Michael Harris), Karen (Jennifer Stock), Lynn (Darcy Brown), and Tom (Jack Neubeck). Prell gives them a presenation on the Yeti, displaying slides with representations of what the unknown beast might look like based on descriptions of supposed eyewitnesses. Prell is planning an expedition with the four graduate students to Boot Island, where his associate Dr. Karl Werner (Tawm Ellis) lives. Werner has told Prell that he suspects a yeti lurks in the woods around his estate, and Prell intends to capture evidence proving the creature's existence. Prell seems particularly interested in Keith, and takes him to dinner at an exclusive restaurant, where he orders a meal for them that isn't on the menu, a special dish called "gin sung".The other students go to a party where they meet a former student of Prell's, Spencer Ste. Clair (Tom Grail). Spencer starts drinking, much to the objection of his wife (Luci Brandt), and when he overhears the students talking about the expedition with Prell, Spencer causes a scene at the party. He becomes hysterical, recounting his own experience on one of Prell's expeditions 8 years prior. Spencer and Prell were the only ones to survive, the others presumably killed by the yeti, which Spencer says attacked him and left him for dead. The people at the party don't take Spencer's story seriously, and he and his wife leave. When they return to their apartment, Spencer's wife breaks his bottle of liquor, causing Spencer to attack her with an electric carving knife. He cuts her throat and then gets into the bathtub, fully clothed, drinking beer. Before she dies, Spencer's wife drags herself into the bathroom with a toaster, which she plugs in and tosses into the bathtub, electrocuting Spencer.Prell and the four students travel by van to Werner's estate, a six hour journey. When they arrive, they meet Werner and his servant, Laughing Crow (Ivan Agar). Werner claims to have had a near encounter with the beast, which he says he hears howling in the woods around the house. He says he smelled a foul odor and heard a very loud heartbeat when the yeti was near. Laughing Crow frightens Karen when she discovers him chopping wood for a fire, and Karen seems particularly sensitive to the potential danger they may encounter. After Prell shows them a map of the island, they plan a route and retire for the evening. That night, Karen hears a strange snarling sound off in the distance.The next day they set out for their destination, some caves where Prell hypothesizes that the yeti may be using for a lair. Before they reach it, they stop to rest and Tom goes off on his own with a rifle, claiming to have seen deer nearby. Prell tells the others he will go ahead to the caves to see if he can see any sign of the yeti. Tom finds a dilapidated barn, where the yeti suddenly appears, leaping onto him and slashing him to death with its claws. When Tom does not return, the others search for him but return to the house at dark.The next morning, the search party resumes but Lynn oversleeps and the others leave without her. During the search, Karen finds Tom's bloody severed leg. Just as they are returning to the house, Lynn decides to explore the greenhouse, but when she goes inside she screams and goes running back out, dashing off into the woods where the yeti follows and kills her. The others find her body and bring it back, storing it in the greenhouse.Prell devises a plan to use Tom's severed leg as bait for the Yeti. Karen is horrified, but Keith still trusts Prell and they go ahead as planned. Prell claims to have been attacked by the Yeti before he could obtain any photos or evidence of it, and they decide to use Lynn's body as bait this time. Karen refuses and keeps telling Keith she wants to leave, but Keith is furious that she does not want to follow Prell's plan. Later she goes into the greenhouse and attempts to move Lynn's body so they can't use her as bait, but instead she finds Tom's body in there. She passes out.When she comes to, she's in bed and the others tell her she simply dreamed finding Tom's body. Eventually she relents and agrees to help get photos of the Yeti using Lynn as bait, but she insists if it doesn't work they all must leave. Prell agrees. The plan almost works, but the Yeti rushes them and nearly grabs Karen. While she is taken back to the house, Keith and Prell rush into the woods after the Yeti. Keith is mystified when he discovers audio speakers wired into the trees, broadcasting the ominous heartbeat of the Yeti. Back at the house, Laughing Crow is playing the heartbeat into the loudspeaker system. Someone knocks Keith unconscious. When he comes to, he goes into the house with a shotgun and confronts Prell and Werner, but Laughing Crow knocks him unconscious again using a large bone. While Werner is distracted making a phone call, Keith comes to again and steals the van, knocking Prell unconscious in the driveway. He drives to the bridge, detouring to hide the van when he notices an oncoming procession of vehicles, apparently headed to Werner's estate.Karen is recovering from the shock of the Yeti attack in her room when she hears the sound it makes outside. When she looks out the window, she sees it running across the grounds toward her window, and it starts to climb right into the room. Panicked, Karen runs through the house with the Yeti after her, growing more and more terrified. Finally she hides in a bathroom and locks the door, but she can't escape. She discovers Laughing Crow inside one of the cabinets, wearing strange face paint and clothing. He emerges with a knife and approaches her threateningly, until Karen lies down on the floor and suffers a heart attack. The Yeti carries her body downstairs and removes its own costume, revealing Werner inside. Prell and Werner congratulate each other on the job they did obtaining their latest "sacrifice".Keith returns to the house with a policeman he managed to flag down, but the cop turns on him and reveals himself to be an ally of Prell and Werner. A diverse group of people have gathered at the estate for this event, which Prell encourages Keith to be a part of. They are a cult of cannibals who come from all walks of life, each of them hosting this festival year after year. The last time Prell hosted was the incident with Spencer Ste. Clair; Prell hoped to induct him into the group, but he "didn't work out", and they left him alive to carry the legend of the Yeti back with him, which allows the cannibals the means to collect victims unnoticed. Prell has the same hopes for Keith, who has already tasted and enjoyed the special "gin sung" dish made of human flesh. At first Keith is resistant, but he is faced with the difficult choice of either being killed by the group or eating Karen's body, and the last shot of the film is Keith drooling over the idea.
question: What was Professor Ernst Prell investigating
answer: The Yeti