- Click really, really fast.
- "Well I'll be!"
To obtain Uncanny Clicker, you have to click 15 times a second (150 clicks in 10 seconds).
As of the 150/10 sec rate, it's difficult to get this achievement the honest way. Only people with very fast clicking can unlock this achievement (function responsible for unlocking this achievement is even called "autoclickerDetected"). The exact rate required has been tweaked multiple times over the development of Cookie Clicker, and may be subject to further changes.
One method of unlocking this achievement is to alternate between two fingers when clicking. This works better with a mouse than a touchpad. Touchpads occasionally detect the different fingers as a swipe and move the cursor across the screen. Another method is tightening your arm muscles while clicking, making your arm 'spaz', allowing you to achieve extreme click rates for a short duration of time. This works better with a mouse than a touchpad.
Hardware assistance can be used to artificially multiply the number of click signals sent, although this is considered cheating by some. The game currently has no way to distinguish a 'real' click from one generated by hardware assistance.
If you use a full keyboard (not a condensed laptop keyboard), you can enable mouse keys to roughly double your rate. To do this, you must press LEFT SHIFT + LEFT ALT + NUMLOCK. Then, simply spam 5 and + on the numpad on the far right side of the keyboard. This has the same effect as alternating between two fingers with a normal mouse.
Many gaming mice have a dedicated double-click button. If you have one, you can spam this button instead of the normal left mouse button to get two clicks per button press.
Another method is available if you have a Graphics Tablet. If you put your tablet stylus pen very close to the surface and tense your muscles in a way that causes your hand to shake, it will make incredibly rapid contact with the tablet's surface, each time counting as a click. It is possible to unlock this achievement in seconds if you can perform this correctly, but it can be quite uncomfortable and is not advised to be performed for sustained gameplay.
On Linux, you can place your mouse cursor over the cookie and execute the following command in a terminal: "xdotool click --repeat 150 1". This simulates 150 mouse clicks using the xdotool program (which has to be installed).
On laptops, if you have a plug in USB or wireless mouse and a right click button, you can click fast enough (on some laptops, the track pad actually clicks twice if pressed once, also adding up.
You can also enable some scripts or otherwise slow your browser down enough that your natural top speed registers higher than it really is.
Outright cheating methods include simply enabling the achievement with a script, or using an autoclicker.