Tohosu are said to have made themselves known to Fon culture initially at mid-eighteenth century (...) Originally born only in the royal family, tohosu were creatures with anomalous characteristics, whose arrival demanded ritual attention. When a Tohosu comes to earth, it is in the body of an abnormal or monstrous infant. For a Tohosu to be born is a sign of discontent, a call to order. Tohosu might be declared at the appearance of any abnormality in a newborn, with signs that ranged from hair and teeth at birth to extreme physical deformities that were typically attributed to the most powerful of the royal tohosu. Even a spontaneous abortion or stillbirth might be considered a tohosu. If recognized, tohosu were said to be returned to the fluid* world from which they had come; their name means, literally, king of the water, in the sense of a marsh or swamp."
*the author previously stated that there might have been a prohibition to spill royal blood, and there was no system to legally depose royalty in Dahomey, which is why when they couldn't be sold into slavery, and simply declared as dead and removed from historical records (many such cases...), the deaths of those coming from a royal lineage had to be in the water, by drowning.
—Wives of the Leopard: Gender, Politics, and Culture in the Kingdom of Dahomey (1998) by Edna G. Bay.