It looks like a regular tree, but the Manchineel can kill you. Everything about it is extremely toxic. If you touch its leaves, they will cause "a strong allergic dermatitis." It's so bad that, if you stay under its foliage while it's raining, the water will cause instant blistering wherever it touches you. It gets much worse.
You can't burn the Manchineel's wood because the smoke will cause temporary and even permanent blindness. And if you eat one of its apples, you can die. Although there's no modern medicine records on any fatalities, there are mentions of deaths in historic records. In fact, Christopher Columbus named it "manzanita de la muerte" or little apple of death for that reason. The poisoning symptoms are horrible:
Ingestion may produce severe gastroenteritis with bleeding, shock, bacterial superinfection, and the potential for airway compromise due to edema. Patients with a history of ingestion and either oropharyngeal burns or gastrointestinal symptoms should be evaluated for admission in hospital.
La manzanita de la muerte.
The indigenous tribes of the Caribbean used the Manchineel's sap to poison arrow tips and leaves to contaminate their enemies' water supplies. It's told that "Spanish explorer Juan Ponce de León was struck by an arrow that had been poisoned with Manchineel sap during battle with the Calusa in Florida, dying shortly thereafter."
If you go on vacation in Florida, the Bahamas, the Caribbean, Central America, or northern South America, avoid getting anywhere near these trees, which are marked with a red band or cross. If not, this may happen to you: