Gorillas totally spooked by something in the grass

Ozala the gorilla mother gets startled by something in the grass. She tries to wipe over it with her arm, which makes Grandma Biddy jump. Ozala is still staring at the grass with her food in her hands and feet. Her eldest son Lope has a quick look as well but then decides to go in. The next clip is of Lope going towards the hut and suddenly moving back, spotting something in the grass. In the third clip, Ozala spots something in the grass and Shufai her youngest quickly decides to climb on mum's back. They both look down into the grass. 4th and last clip, Lope sits at the hut, when he moves, something in the grass stops him in his tracks. The only thing I can think of would be insects in the grass. What do you think?