Continuity mistake: When Johnny Cage is fighting Scorpion, and he does his human spear, Johnny runs until he stops at the tree. The spear then catches up, and becomes wrapped around the tree in front of Johnny. When the camera changes view, the spear is just leaning on the tree. The camera changes view again and the spear is wrapped around the tree again. When Scorpion pulls the spear back, it goes straight back, and doesn't unwind around the tree.
Continuity mistake: In the final fight (Liu Kang vs Shang Tsung), after Liu Kang has defeated the five people Shang Tsung made appear, Liu goes to the middle of the floor (and MK logo) and says "Is that all you've got, sorcerer?" Immediately after this line, the camera angle (and shot) changes, and if you pay attention to the MK logo on the floor, notice that Liu Kang turns 90 degrees between the shots without taking a single step. (01:20:35)
Continuity mistake: When Liu Kang fights Sub-zero, Liu Kang stands in a fighting position with his left hand in front of him while Sub-zero generates a lot of ice. Just before the ice hits Liu Kang, the shot changes and Liu Kang stands opposite with his right hand in front of him. (00:53:05)
Continuity mistake: When Johnny Cage goes to kick Scorpion in the forest, he leads with his left foot but after they teleport he falls with his right leg extended.
Continuity mistake: When Shang Tsung has finished summoning his warriors, before the last fight with Liu, the camera zooms out showing all five warriors, you can see Shang lowering his arms to his sides. Then it shows a close-up of Shang Tsung and he has his arms in the air and lowers them again.
Continuity mistake: When Kano is talking to Goro, he is drinking from a large goblet, and it is the only one on the table. Goro knocks the drink onto Kano's lap, and the camera cuts to Goro saying, "How lucky for them, back home." The camera cuts back to Kano and the goblet is sitting back on the table. The camera cuts to Shang Tsung entering the room and back to Kano with the goblet correctly missing.
Continuity mistake: In the fight with the ninjas where Lu and Cage are fighting 3 guys each while Sonya only fights one, there's a shot where Cage grabs a guy with a spear extended out by his right arm. In the next shot, it's on his left side instead.
Continuity mistake: When Lui and the others are walking up to Raiden during the ending, we see a cute shot of Johnny putting his arm around Sonya. The movie then cuts to a wideshot, and he puts his arm around her a second time.
Continuity mistake: During the ending, watch Liu and Kitana closely as Raiden says the line "I've been looking for you! What took you so long?" Kitana has her arm around Liu's, but lets go and stands a few feet away from him. The camera then cuts to a medium-shot of Liu and Raiden talking. (Kitana is not visible in this shot, as she is standing several feet away.) Then, the camera cuts again to a wider shot, and suddenly Kitana is standing literally right next to Liu and has her arm around his once again.
Answer: Since the entire fight is focused on Liu Kang and Reptile, he could have possibly waited to see what the outcome of the fight was.