Taurine
An amino acid in energy drinks; now almost always synthetic, though historically from ox bile.
Why this is a critical point
Taurine was historically extracted from ox bile (the name comes from the Latin word for "bull"). Modern production is almost entirely chemical synthesis, which is generally safe, though the stated source is still worth checking with unverified manufacturers.
Halal alternative
Halal-certified synthetic (chemically manufactured) taurine.