25NL A4o 2pair what do these donk-bets mean?

[Triggerle]

EverestPoker Game #1305394862: Table Muscat-4 - $0.15/$0.25 - No Limit Hold'em - 18:32:19 - 2007/03/25
Seat 1: UTG ($5.48)
Seat 2: MP ($11.46)
Seat 3: CO ($12.01)
Seat 4: Hero (Button) ($25.00)
Seat 5: SB ($29.54)
Seat 6: BB ($15.50)

SB posts the small blind of $0.15
BB posts the big blind of $0.25
MP posts $0.25

*** HOLE CARDS ***
Dealt to Hero[4/images/graemlins/spade.gif A/images/graemlins/heart.gif]
UTG folds, MP checks, CO folds, <font color="red">Hero raises to $1.15</font>, SB folds, BB calls $0.90, MP folds.

*** FLOP *** ($2.70) [4/images/graemlins/heart.gif K/images/graemlins/diamond.gif A/images/graemlins/club.gif]
<font color="green">BB bets $0.25</font>, <font color="red">Hero raises to $2.00</font>, BB calls $1.75.

*** TURN *** ($6.70) [4/images/graemlins/heart.gif K/images/graemlins/diamond.gif A/images/graemlins/club.gif] [3/images/graemlins/diamond.gif]
<font color="green">BB bets $0.25</font>, <font color="red">Hero raises to $4.00</font>, BB calls $3.75.

*** RIVER *** ($14.70) [4/images/graemlins/heart.gif K/images/graemlins/diamond.gif A/images/graemlins/club.gif 3/images/graemlins/diamond.gif] [5/images/graemlins/diamond.gif]
BB checks, Hero checks.

[Paul Thomson]

probably a weak ace. i'd value bet river.