The ball was heading wide but, unfortunately for the visitors, it struck Knight's leg and trickled into Jussi Jaaskelainen's net.
Four minutes into stoppage time, Harris netted his second goal when heading the ball home following a cross from veteran fellow frontman Steve Claridge.
That initial spurt of pressure saw Liverpool win a corner with Maxi Rodriguez heading the ball to Torres, but the Spanish striker's volley struck the post.
Snapdragon has already built working game demos featuring this technology, including a soccer game that allows players to score a goal by heading a ball into a net.
Spurs argued at the award of a Chelsea corner as they believed Joe Cole was offside when Essien took his shot prior to Jonathan Woodgate heading the ball out.
Bafetimbi Gomis lobbed in the fourth after heading the ball past Debrecen goalkeeper Vukasin Poleksic early in the second half, as Lyon established a three-point lead over Liverpool and Fiorentina at the top of the group.
When a young Kevin Keegan was honing the skills that would make him a football superstar in the 1970s and 1980s, he spent hours kicking and heading a ball against a wall, and trapping and controlling the rebounding football.
St Johnstone were more enterprising at the start of the second half and Samuel should have scored when he latched on to Cleveland Taylor's cross but the striker elected to stretch out a foot instead of heading the ball and the effort was collected comfortably by keeper Brown.
After an uneventful opening, Chelsea launched an innocuous-looking attack with Deco heading on a ball that hugely favoured the home keeper, but when James's kick met air instead of ball due to a large bobble off the turf, Drogba was able to run on and slot into the unguarded net.
The France centre pretended to ground the ball before getting to his feet and heading nearer the posts, getting a clip from Gareth Williams for his cheek as he finally touched the ball to grass.
Conway's attempted shot looked to be heading wide but Robertson flicked the ball awkwardly towards goal and tried to follow it in before McGregor punched clear on the goal-line, United unable to make anything of the rebound.
On 59 he hooked Siddle to the square-leg boundary, Shane Watson took the catch but realising he was heading over the rope he parried the ball upwards but could not prevent it going for six.
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But, the very next ball, England's talismanic all-rounder was also heading back to the pavilion, the victim of a poor decision by Tiffin when trapped by a Zaheer delivery that pitched outside the line of leg-stump.
To make matters worse, their neck muscles aren't as well developed and they often lack the correct heading technique that can help dissipate the force of the ball.
His low drive from the edge of the area looked to be heading wide, but the deflection off Neil Taylor's boot sent the ball in the opposite direction and past the wrong-footed Michel Vorm in the Swansea goal.
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