Bob deposits 5 ETH and 4 ETH worth of YFI, and borrows 5 ETH worth of DAI
If Bob’s Health Factor drops below 1 his loan will be eligible for liquidation.
A liquidator can repay up to 50% of a single borrowed amount = 2.5 ETH worth of DAI.
In return, the liquidator can claim a single collateral, as the liquidation bonus is higher for YFI (15%) than ETH (5%) the liquidator chooses to claim YFI.
The liquidator claims 2.5 + 0.375 ETH worth of YFI for repaying 2.5 ETH worth of DAI.