You shouldn't use your finger. From the Arctic Silver application guide:
Important: Keep the surface free of foreign materials and do NOT touch the surface after it has been cleaned. A hair, piece of lint, and even dead skin cells can significantly affect the thermal interface's performance. Oils from you fingers can adversely affect the performance by preventing the micronized silver or ceramic fill from directly contacting the metal surfaces. (Fingerprints can be as thick as 0.005")
Pea size is WAY too much. WAAAAAAY too much. You want maybe 1/4 that. You can spread it yourself if you want - doesn't matter - but I wouldn't use my finger. Personally, I put 5 very small dots of it in an X style.
Did you miss the "small" part? I've seen some pretty small peas!
I've used "rice" sized, and when removing later notice it was not sufficiently spread to all parts of the chip. "Small pea" sized blob works beautifully every time!
I put a glob in the middle so it squeezes out covering everything for a few inches!
yeah right I use a tooth pick and stick it into the tube and smear it around evenly the place the hsf and forget it, it hasn't failed me yet.
When I remounted the CPU's heatsink, I reapplied a single vertical line (with respect to the lettering on the CPU's heat spreader) after tinting both of the contact surfaces with a little AS5. (Tinting means applying just enough to cover all of the contact surface after it is spread by an old credit card, and then wiping the stuff off so that the application is barely evident.)