I've never understood that last one. Assuming I am otherwise physically healthy and don't have any foreign objects in my mouth, I can't really taste anything but neutrality. Technically I can probably taste saliva, but I think my brain filters that out and noting it doesn't seem like it would help anyway.

Unless I'm misinterpreting and I'm supposed to go lick something during a panic attack. I know I've read that biting into a lemon can help.