Sherlock engaged John in conversation, whilst Mycroft texted on his phone.

(Electromagnetic Pulse (EMP). EMPs disable electronics momentarily. The way to become immune to toxins is to take a little bit at a time, slowly increasing the doses. I did it with Nicotine so I can't get poisoned by it. But I'm not addicted either.)

(oh wow! Didn't know about that. Sounds good)

She finished making it, especially adding the poison and extra hazelnut to Mycroft and rushed over, careful not to spill any and put it down in front of them
(Is this.. allowed?)

(Yesh.)
Mycroft took a sip from the poison and gagged. "This is the worst espresso! What is in this?!" he sputtered.
John fell out of his seat, laughing. Sherlock smirked.

She smiled and looked back, "Is something wrong, Sir?"

"Oh... nothing." Sherlock said, blushing. "It's just my brother's reaction." he took a sip of his own coffee and did the same. John fell out of the seat, and this time Mycroft smirked.
"GROSS!!!!" Sherlock bellowed.
John took a sip of his non-tampered tea and looked at the two brothers. "Something wrong with the drink? She got mine perfect. Best cuppa I ever had, this." he pointed to his own drink.

"Thank you, Sir." she smiled gently, "it'd be polite to drink it whether you liked it or not, or would you prefer a lecture?"

Link: https://www.sylestia.com/forums/?thread=50820&page=28#276 Author: Nafariaandulin Time Posted: 9/15/2017 at 1:40 PM Life at 221c Baker Street was rather dull. Every morning you woke up to the same life that you'd always had, until one day, while you came back from your job to find your house ransacked with a dead man on your floor and a note that read: I'm back - JM

i carefully step around the dead man. and head to the phone then i call 911

"Ahem. Luna is here." Another voice suddenly piped up in the direction of the couch. What was previously empty, now a girl with long black hair in a ponytail wearing a black jumper, shirt, skirt, sneakers and thin gloves lounged in it. She wore a thin veil, concealing her face.
"Hi! You've got your part in preps done, I suppose?" Destiny asked, striding up to the couch and poking Luna in the stomach.
"Duh, of course I have. Mom..." Came the reply.

(Not really her mom; ya know, it's teasing.)

IGNORE THIS IF YOU DON'T LIKE SCIENCE AND/OR YOU DON'T LIKE BEING PROVEN WRONG
You should also ignore this because I was extremely bored and this is just a random rant. Random fact: I sometimes have a habit of pointing out people are wrong.
Don't get angry at me or hate me; I was bored :(
(Then again, what I say below may be wrong...)

Quote (Post 45):
"Who are you?" the man who must be DI Lestrade asked, looking at you. "I thought I told Anderson not to let anyone through."
"Anderson has the prose of white noise." Sherlock said. "You shouldn't put him up to such simple tasks."
"Anderson speaks highly of you too." Lestrade replied. "Apparently, you're the only one he'd do a post-mortem on in his own time."
"If his knife is as sharp as his intellect, he can name the date." Sherlock responded. "Cause of death?" he asked, kneeling over a bloody mass of what looked like part of a human being.
"Uh-Explosives." Lestrade said.
"Wrong, have you even smelled this body? It has a citrus-like scent. Poison. This person was dead before they were blown up." Sherlock said. He glanced up at you. "Have any ideas on what poison it is? I like taking turns."

I'm going to assume Sherlock sniffed the body.

(Firstly: Trichloroethane is not considered a poison)

I did some research on trichloroethane, and the results were... well, let's say, weird. Okay. So Sherlock sniffed the body. That's bad (maybe not in this case, but ya know, just taking precautions). According to the MMG, inhalation of trichloroethane can be pretty dangerous (in high concentrations). At normal levels of inhalation, it can cause headaches/dizziness/loss of coordination (Quote from other website: "Short exposure could cause serious temporary or moderate residual injury"). Longer exposure to this chemical can cause a lot of more serious problems such as cardiac arrest, a coma, or even death, etc. Then again, this compound contains a lot of chlorine so it wouldn't smell like citrus. Especially since the compound is slightly more basic instead of acidic. According to a couple of medical sites, trichloroethane smells more like chloroform.

Now, all of that is if the chemical used was actually 1,1,1-trichloroethane. If it was 1,1,2-trichloroethane, you could expect one to be dead/fatally poisoned.