Herbert S. Terrace was sceptical of the so-called language-use by Washoe, Sarah and Lana. He compared the abilities of the apes with those found in pigeons which are taught to peck keys in a specific order. All apes signed only to receive reward from their trainers. If you have a look at the first and mostly used words of the animals in the projects you will find that they are almost all related to food, drink and other desirable activities like tickling and chasing.
Therefore Terrace raised and trained Nim Chimpsky (named after the famous linguistic theorist Noam Chomsky who stated that the predisposition for language acquisition is innate). The method was the same used with Washoe and Nim learned about 125 signs. He demonstrated some syntax by using the verb more frequently before the object than vice versa (e.g. "hug Nim" instead of "Nim hug"). Nim did apply some of the signs in a new context (e.g. DIRTY when he had to go to the toilet). He also warned people by using the signs for ANGRY and BITE and tended not to attack if this warning was heeded.
But by analysing the videos of the training sessions Terrace found that Nim's signs often were imitations of the signs the trainer first used. Terrace et al. (1979) concluded that there was little evidence that Nim was actually using language. They also found out by analysing Washoe's videos that she mimicked the trainer like Nim did.
Nim is now retired and lives at the Black Beauty Ranch of the Fund for Animals. Click here for an article about him and the other chimps living there.