Complex sentence: It is estimated that only 10 to 15 mg will kill a human adult; however, its bites deliver about 120 mg of venom on average, although they may deliver up to 400 mg of venom in a single bite.
Split into simpler sentences: It is estimated that only 10 to 15 mg will kill a human adult, and its bites deliver about 120 mg of venom on average. Although they may deliver up to 400 mg of venom in a single bite.