My dog has a black spot in the middle of its tongue; it wasn’t there before.

Sudden black spots on a dog’s tongue are mainly from melanin deposition; if eating, defecating, and spirits are normal, it is generally a normal phenomenon. Some black spots come from drugs like broad-spectrum antibiotics causing black coating. Others are blood stasis from a prick, appearing black and healing in 7-14 days. If appetite and spirits drop, check for oral or endocrine disease causing the spots.