The filmmakers watched videos of real Makos swimming frame by frame then borrowed equipment and technology that's typically used in Boeing 747s and built the sharks as self-contained units. The remote controlled machines had one thousand horsepower engines, weighed eight thousand pounds, and swam on their own without the use of external wires or apparatus, up to thirty miles per hour. They built four and a half sharks: three fifteen-foot Makos, which played the first gen sharks; and one and a half generation-two sharks, which represented that first generations twenty-six-foot-long progeny, the effect was quite realistic: Stellan Skarsgård remarked "The first time I saw one of those animatronic sharks I thought it was a real one." Samuel L. Jackson recalled "when they first brought the animatronic shark into the lab we were all in awe of the size of this machine. It was a real monster. I would walk up to it slowly and touch it, and they said it felt like a real shark. The gills moved and it had a mind of its own sometimes." Renny Harlin recounted "one shark was sitting in McAlester's room, and just as we were getting the computer programming finished, all of a sudden it leapt up and went through the ceiling. All these 2x4s flying away like matchsticks. It gave us an idea of the awesome power of these creatures and how careful we had to be in terms of the cast and crew being close to them, and how the computer program had to have failsafe procedures so nobody got hurt."