I always thought that thought speak was one-sided with humans, and that the Animorphs could only communicate back in thought-speak when they were in morph. However, I've just finished re-reading #1 Invasion, and when Elfangor is explaining things to the Animorphs before he dies, the group asks if Visser Three can "hear" their thoughts. To answer their question, Elfangor says he cannot hear their thoughts, directly followed by Visser Three taunting Elfangor. How did Elfangor hear them to answer the question though? Also, in Jake's room Tobias was demonstrating morphing by becoming his cat, Dude. Jake started hearing Tobias's thought-speak and he made the assumption that thought-speak only works when in a morph. Then, Jake kind of thought toward Tobias and asked if he could hear what he's thinking. Tobias said that he could only hear the thoughts if Jake "thought at him."
My question: Does one have to be in morph to speak through "thought-speak?" (Assuming we're talking about the humans, the Animorphs)