AN 9.1: asubha, metta, 16 APS, anicca-sañña are 4 indispensable practices
|Non-beautiful [foulness perceptions] (he) should-develop,|
|(for) [lustful] passion's removal,|
|Good-will (he) should-develop,|
|(for) ill-will's removal,|
|inhale-exhale-mindfulness (he) should-develop,|
|(for) [distractive] thinking's-cutting-off,|
|im-permanence-perception (he) should-develop,|
|(for one who has) Im-permanence-perception, monks,|
|not-self-perception (is) established.|
|(for one who has) not-self-perception,|
|pride-(and)-conceit's-uprooting (is) attained,|
diṭṭheva dhamme nibbānan”ti.
|here-and-now (is) Nirvana."|
16APS great for driving out thoughts, like juggling...If you do a challenging and/or very interesting activity, like juggling, it requires all of your attention devoid of thinking to focus on the action required. Similarly, the reason 16 APS is such an effective tool for removing thought, is it requires all of your attention and focus, and relaxation to become sensitive to the tactile experience of breath in every cell of our body. That's what's meant by step 3 of 16 APS. Like a Chinese medicine doctor holding your wrist and listening to your pulse carefully, or juggling a sufficiently challenging number of objects that it requires all of your attention with no spare bandwidth for thinking or mental commentary.
That's how you can know you have a second jhana. When the sensitivity of the tactile experience of every cell in the body, coupled with piti and sukha, is clear, uninterrupted force pervading everywhere.