They watch dwell time to see whether readers stay engaged after opening sponsored content. Scroll depth, hover activity, and swipe speed hint at curiosity or boredom. Repeat visits and return frequency suggest stronger purchase intent, while rapid exits can lower perceived quality. Networks also compare how users react across devices, locations, and times of day to predict conversion likelihood. Quiet signals like muted videos, skipped placements, or delayed interactions help algorithms estimate genuine attention instead of accidental taps. Combining these patterns helps advertisers bid more confidently for audiences likely to convert.