Telepathic Conversations occur between members of the group, because, as Future Ted explains, they know each other so well that they can each communicate telepathically with one another.
However, not all these conversations are successful, since one person can easily misunderstand what the other is saying.
Also, one or more members of the group can be kept out of the conversation, for example, Ted doesn't understand them when Marshall, Lily and Robin talk telepathically about how to talk Ted into dyeing his hair blonde, and Lily doesn't "hear" him, when Marshall stops the others telepathically from telling Lily that the Pretzel Vendor is not Barney's doppelganger. (Doppelgangers)
It first occurs between Ted and Marshall in Mary the Paralegal, and has become a recurring element throughout the series.
Telepathic Conversation Episodes
The following episodes have had telepathic conversations occur between two or more people.
Ted and Marshall have a telepathic conversation in regards to Sandy Rivers being Robin's date. Later, Marshall tells Lily that Ted's date Mary is a hooker, telepathically, so no-one else can hear him say it. She then accidentally announces it out loud.
Lily and Robin have a telepathic conversation where Robin tries to communicate to Lily that she should not open her gift in front of her family. Robin expresses surprise at the technique working, however, after the conversation, Lily's mom hands Robin a tampon, showing that there was apparently a substantial miscommunication between the two.
Ted and Stella have a telepathic conversation when they discuss if they have to help the sister of Stella, Nora. However, Ted thinks Stella simply means to pick up the check for dinner; Stella means that they should get married in the wedding her sister had planned.
Ted tries to convince Barney that they need to close the bar. But Barney merely responds with the song "Kokomo" (The Beach Boys). Ted is convinced.
Marshall, Lily and Robin have a telepathic conversation in front of Ted to discuss how to best convince him to dye his hair blonde. Ted realizes what they're doing, however he incorrectly guesses the conversation topic and thinks they're talking about ordering nachos. Later on Marshall, Lily and Barney have another discussion about Ted's hair and how it actually looks really good.
Marshall also stops the others telepathically, when the are about to tell her that the guys Lily thinks is Barney's doppelgangers doesn't look like him, at all.
When Marshall and Lily tell the rest of the gang they're pregnant, Marshall begins to have a panic attack, and hopes Lily can't tell what he's thinking. Through a telepathic conversation, she can, and tells him that she's freaking out too, and they talk about how to hide their fear from the rest of the gang.
After Marshall and Lily run into Daryl LaCoutre at Wesleyan and he invites them to his house, Marshall and Barney have a telepathic conversation to discuss that if he unjinxes Barney, he can lie them out of going to Daryl's house.
Barney and Robin have a telepathic conversation about "taking care" of Ranjit as he knowns that they might be related.
Robin and Lily and then later Ted and Barney share a telepathic conversation about Darren.
Ted and Gary Blauman had telepathic conversation for feuding over one girl who loved the autobiography of Teddy Roosevelt.